Nonneoplastic Diseases of the Prostate

Zonal Anatomy

The prostate is composed of three zones: the peripheral zone, central zone, and transition zone ( Tables 8.2 and 8.3 ; Fig. 8.2 ). The peripheral zone contains approximately 70% of the volume of the prostate and is the most common site of prostatic intraepithelial neoplasia (PIN) and carcinoma. Peripheral zone acini are simple, round to oval, and set in a loose stroma of smooth muscle and collagen ( Fig. 8.3 ). Digital rectal examination often includes a description of the left and right “lobes” based on palpation of the median furrow in the midline that divides the peripheral zone into left and right halves.

The central zone is a cone-shaped area that includes the entire base of the prostate and encompasses the ejaculatory ducts; it comprises approximately 25% of the volume of the prostate. A recent report using magnetic resonance imaging (MRI) found that, contrary to McNeal’s classical anatomic teachings, the central zone extends below the verumontanum in 95% of men older than 43 years of age, likely because of deformation of the prostate by nodular hyperplasia. Central zone acini are large and complex, with intraluminal ridges, papillary infoldings, and occasional epithelial arches and cribriform glands mimicking PIN ( Fig. 8.4 ). The ratio of epithelium to stroma is higher in the central zone than in the rest of the prostate, and the stroma is composed of compact interlacing smooth muscle bundles.

The transition zone contains the smallest volume of the normal prostate, approximately 5%, but it enlarges together with the anterior fibromuscular stroma to massive size in benign prostatic hyperplasia (BPH) and dwarfs the remainder of the prostate (discussed later). Transition zone glands tend to be simple, small, and round, like those in the peripheral zone, embedded in a compact stroma that forms a distinctive boundary with the loose stroma of the peripheral zone ( Fig. 8.5 ). The stromal extracellular matrix contains collagen types I, III, IV, and V, fibronectin, laminin, chondroitin sulfate and heparan sulfate proteoglycans, and elastic fibers. The central zone and peripheral zone are often referred to together as the outer prostate or nontransition zone, whereas the transition zone and anterior fibromuscular stroma are often referred to as the inner prostate.

Gene expression differs between the peripheral zone and the transition zone, and stromal-epithelial interactions may be responsible for the distinct zonal predilection for select diseases, especially cancer. For example, ERG and ETV1 are upregulated in the glands of the peripheral zone compared with the transition zone; this finding may be important when considering that ERG and ETV1 fusions are found in 80% and 20% of prostate cancers, respectively. Stromal cells from the peripheral zone have a greater capacity to induce development and progression of cancer than those from the transition zone through growth factors regulated by sex hormones.

Prostatic Urethra, Verumontanum, and Bladder Neck

The urethra serves as a reference landmark for the study of prostatic anatomy ( Fig. 8.2 ). A single 35-degree bend in the center of the prostatic urethra creates proximal and distal segments of nearly equal length. The verumontanum bulges from the posterior wall at the urethral bend and tapers distally to form the crista urethralis. Most prostatic ducts and the ejaculatory ducts empty into the urethra in this part of the middle and distal prostatic urethra, whereas the small periurethral glands of Littre have minute openings throughout the length of the urethra.

Just proximal to the verumontanum is the utricle, a small, 0.5-cm-long epithelium-lined cul-de-sac derived from the urogenital sinus, in contrast with the previous belief that the utricle is a müllerian remnant. Careful microdissection study revealed three types of utricle based on the location of its pouch; in the most common type, the utricle projected out from between the two ejaculatory ducts. The site and shape of the utricular orifice were also diverse; this orifice was most commonly located on the distal three-fourths of the prostatic urethra.

A circumferential sleeve of muscle surrounds the entire urethra. This muscular layer includes a proximal preprostatic smooth muscle sphincter that prevents retrograde ejaculation and a distal sphincter of striated and smooth muscle at the apex that is important in control of micturition.

At the bladder neck, there are three muscle layers: submucosal longitudinal, circular bladder neck, and external longitudinal muscles. Increased prostate volume correlates with an increase in collagen fibers and thinning of muscle in the anterior neck, as well as degeneration of the posterior neck. Nodular hyperplasia increases the amount of fibrosis, with circular muscle fibers becoming thin and fragmented.

Capsule and the Retroprostatic Fascia (Denonvilliers Fascia)

The capsule of the prostate consists of an inner layer of smooth muscle and an outer covering of collagen, with marked variability in the relative amounts in different areas ( Fig. 8.6 ). The collagenous fascia surrounding the prostate is multilayered, consisting of collagen, elastin, and smooth muscle fibers, and may fuse with the muscular capsule depending on location and individual variation.

At the apex, acinar elements may be sparse, and the capsule is ill-defined, composed of a mixture of fibrous connective tissue, smooth muscle, and striated muscle. As a result the prostatic capsule cannot be regarded as a well-defined anatomic structure with constant features, especially at this location. In biopsy and surgical specimens the capsule at the apex and bladder base is difficult to identify; consequently, it is often not possible to determine the presence of extraprostatic extension when cancer is present at these sites.

At the lateral aspect of the prostate the pelvic fascia and the prostatic capsule are separated by adipose tissue in 52% of cases, but are adherent without fat in the remainder. Anteriorly there is a smooth transition from the capsule to the anterior fibromuscular stroma, but the capsule is recognizable at this location in only 11% of cases. The lateral pelvic fascia connects and fuses with the anterior fibromuscular stroma, and covers the outermost regions of the lateral and anterior surfaces in 85% of cases.

Posteriorly the retroprostatic fascia (Denonvilliers fascia) separate the prostate, seminal vesicles, and bladder from the rectum, with significant interindividual and site-specific variation. The fascial muscular bundles and collagenous fibers posterior to the vas deferens blend with central zone stroma and the ejaculatory duct sheath at the junction of the base of the prostate with the seminal vesicles and vas deferens. The retroprostatic fascia is fused with the capsule at the center of the prostatic posterior aspect in 97% of cases.

Abundant adipose tissue is present around most of the prostate and is a reliable marker of extraprostatic tissue, present on 48% of all prostatic surfaces examined in whole-mount specimens. The distribution varies among the different surfaces of the prostate, with the anterior, posterior, right, and left surfaces showing 44%, 36%, 59%, and 57% adipose tissue, respectively. Nerve-sparing prostatectomy resulted in slightly less adipose tissue (46%) than did non–nerve-sparing procedures (54%).

Intraprostatic fat is rarely observed and, when present, consists of a small, microscopic focus of a few adipocytes. For practical purposes, identification of fat in biopsy specimens is considered sampling of extraprostatic tissue.

Blood Supply

The blood supply of the prostate is furnished by a branch of the internal iliac artery. The most frequent origin is the internal pudendal (56% of cases), followed by the common gluteal-pudendal trunk (28%), the obturator (12%), and the inferior gluteal (4%). Anastomoses are present at the termination of the internal pudendal artery in 24% of cases, with the contralateral arteries in 12%, and to the superior vesical artery in 8%. The two main arterial pedicles to the prostate from each hemipelvis are the superior and inferior prostatic pedicles. The superior pedicle provides the main arterial supply of the gland and includes branches to both the inferior bladder and the ejaculatory system. The inferior pedicle distributes as a plexus in the apex and anastomoses with the superior pedicle. Prostatic and capsular arteries run along the lateral border of the prostate and serve as a visual landmark in the majority of cases for cavernosal nerve-sparing prostatectomy. Arterial embolization provides symptomatic control in patients with nodular hyperplasia.

Veins drain directly into the prostatic plexus, and an extensive arborizing network is present in the capsule. The venous drainage empties into the internal iliac vein. Lymphatics from the prostate drain mainly into the internal iliac lymph nodes, with lesser drainage into the external iliac and sacral lymph nodes. Antibodies directed against lymphatic vessel endothelial hyaluronan receptor (LYVE1) revealed that lymphatic density was greater in nodular hyperplasia than in carcinoma, whereas microvessel density with anti-CD34 antibodies revealed the opposite.

Nerve Supply

The nerve supply of the prostate is furnished by paired neurovascular bundles that run along the posterolateral edge of the prostate from apex to base, embedded between the fascial layers covering the prostate and seminal vesicles. These bundles consist of numerous nerve fibers on a scaffold of veins, arteries, and variable amounts of adipose tissue surrounding almost the entire lateral and posterior surfaces of the prostate. At the apex and the urethra, the neurovascular bundles have two divisions: cavernous nerves (continuation of the anterior and anterolateral fibers around the apex of the prostate on the way to the corpora cavernosa) and corpus spongiosum nerves (continuation of the posterolateral bundles that eventually reach the corpus spongiosum). Surgical sparing of these structures during radical prostatectomy preserves sexual potency. Variation in size and shape of the prostate influences the anatomy of the neurovascular bundles, the urethral sphincter, the dorsal vascular complex, and the pubovesical and puboprostatic ligaments.

Autonomic ganglia are clustered near the neurovascular bundles, with small branching nerve trunks that arborize over the surface of the prostate, penetrate the capsule, and divide to form an extensive network of nerve twigs within the prostate that is often in intimate contact with the walls of ducts and acini. Capsular ganglia are present in 52% of prostates, most frequently at the posterolateral aspect of the base. No obvious differences exist between capsular and periprostatic ganglia. Pacinian corpuscle has also been found in the prostate. The posterior capsule has more nerve fibers than the anterior capsule according to S-100 protein staining.

Caution is warranted in interpretation of perineural space invasion as an absolute criterion for the diagnosis of cancer because this feature can be seen rarely in benign glands ( Fig. 8.7 ).

Nerve fiber density is greater in the peripheral zone than in the transition zone, especially in patients with BPH, according to S-100 protein immunohistochemical study. The posterior capsule has significantly more nerve area than the anterior capsule. Innervation appears to decrease with age.

Needle Biopsy

The introduction of the automatic spring-driven 18-gauge core biopsy gun three decades ago began a new era in the sampling of the prostate for histologic diagnosis ( Fig. 8.8 ). The 18-gauge needle offered important advantages over the older 14-gauge needle. The rate of postbiopsy infection declined from up to 39% to less than 1%, and hemorrhage with urinary clot retention declined from 3% to less than 1%. In recent years the postbiopsy sepsis rate has risen, probably because of increased antibiotic resistance ranging from 3% to 5%. The false-negative rate declined from up to 25% to 11%, and the quality of the tissue sample improved, usually with little or no compression artifact at the edges. The main disadvantage of the 18-gauge needle is that it provides less than one-half as much tissue per needle core for pathologic examination as the traditional 14-gauge biopsy. One report found no difference in cancer yield between 16-gauge and 18-gauge needle biopsies. A recent study found that longer and consistent cores were obtained using novel elongate 15- and 17-gauge biopsy needles that included peripheral and anterior zone tissue sampling in a single core, enhancing determination of cancer location for focal therapy planning.

Current clinical guidelines recommend that extended biopsy schemes with 10 to 12 specimens be obtained. Segregation of specimens into individual vials improves specimen handling, enhancing tissue representation and diagnostic accuracy. Also, focal prostate cancer treatment strategies depend on more precise tumor mapping, requiring even greater tissue sampling. Saturation biopsy using the 18-gauge core biopsy gun significantly increases cancer detection rate over methods with six or fewer cores. In recent years the number of positive biopsies with only small foci of cancer has increased because of the success of early detection efforts in identifying smaller tumors at earlier stages. Frequently we encounter small, suspicious foci in biopsies from asymptomatic young men who have no palpable abnormality and only slight elevation of serum prostate-specific antigen (PSA) concentration; this issue is discussed in Chapter 9 .

Inking the needle biopsy specimen is useful for identifying tissue cores in paraffin blocks, but this is infrequently performed, although we do this routinely. We found that submission of three cores in a single cassette was equivalent to one core per cassette for cancer detection, despite additional sectioning of the one-biopsy-core-per-cassette blocks. No significant increase occurred in level of detection of atypical small acinar proliferation and adenocarcinoma with greater sampling. Consequently, we now recommend submission of three cores per cassette to minimize labor and cost of processing. However, this recommendation differs from that of the European Society of Uropathology, which prefers separate processing of each core but provides no data to bolster its beliefs.

Laboratories also vary in the number of serial sections obtained from prostate tissue blocks for routine examination. We routinely obtain six sections on each slide from three levels (two sections per level) ( Fig. 8.9 ). A minimum of two slides is prepared: slide 1 for hematoxylin and eosin (H&E) stain, and slide 2 for potential special studies such as immunohistochemistry for keratin 34βE12/p63/racemase/c-myc. In our experience, recutting the block for additional levels is useful in approximately one-half of cases, because refacing of the block results in further loss of tissue, with usually no more than four additional slides before the specimen is exhausted. Other aspects of tissue processing and handling were recently reviewed.

Fine Needle Aspiration

Fine needle aspiration remains popular for cytologic examination of the prostate in parts of Europe and around the world, but interest in this method in the United States has dropped precipitously because of the ease of acquisition and interpretation of the 18-gauge needle core biopsy. Both techniques have similar sensitivity in the diagnosis of prostatic adenocarcinoma, and both are limited by small sample size; they are best considered complementary techniques. Complications of fine needle aspiration occur in less than 2% of patients and are similar to complications of biopsy, including epididymitis, transient hematuria, hemospermia, fever, and sepsis.

Fine needle aspiration produces clusters and small sheets of epithelial cells without stroma ( Fig. 8.10 ). This enrichment for epithelium allows evaluation of single cells and the architectural relationship between cells. Benign and hyperplastic epithelia consist of orderly sheets of cells with distinct margins creating a honeycomb-like pattern. Benign nuclei are uniform with finely granular chromatin and indistinct nucleoli; basal cells are often present at the edge. Carcinoma is distinguished from benign epithelium by increased cellularity, loss of cell adhesion, variation in nuclear size and shape, and nucleolar enlargement. Fine needle aspiration is not usually used as a screening test for prostate cancer. However, the specimen obtained from fine needle aspiration can be used for other diagnostic and prognostic testing, such as morphometric analysis, DNA ploidy, cytogenetic studies, and molecular diagnostics. Ductal adenocarcinoma may be diagnosed by fine needle aspiration combined with immunohistochemistry.

Imprint cytology of biopsies also relies on the evaluation of single cells and clusters. Compared with histologic findings, imprint cytology had accuracy, sensitivity, specificity, positive predictive value, negative predictive value, false-positive rate, and false-negative rate of 98%, 97%, 98%, 93%, 99%, 2%, and 3%, respectively.

Transurethral Resection

The regions of the prostate sampled by transurethral resection (TURP) and needle biopsy tend to be different. TURP specimens usually consist of tissue from the transition zone, urethra, periurethral area, bladder neck, and anterior fibromuscular stroma ( Table 8.3 ). Studies of prostatectomies performed after TURP show that the resection does not usually include tissue from the central or peripheral zone, and not all the transition zone is removed. Most needle biopsy specimens consist only of tissue from the peripheral zone and seldom include the central or transition zones or anterior stroma.

Low-grade adenocarcinoma found incidentally in TURP chips usually has arisen in the transition zone. These tumors are frequently small and may be completely resected by TURP. Poorly differentiated adenocarcinoma in TURP chips usually represents part of a larger tumor that has invaded the transition zone from the peripheral zone.

The optimal number of chips to submit for histologic evaluation from a TURP specimen remains controversial; some authors advocate complete submission even with large specimens that require many cassettes. The College of American Pathologists recommends a minimum of six cassettes for the first 30 g of tissue and one cassette for every 10 g thereafter.

Tissue Artifacts

Cautery artifact is frequently extensive in TURP specimens and often limits interpretation, particularly at the edge of chips. The epithelium usually shows more damage than the stroma, with separation from the basement membrane, cellular disruption, loss of integrity of nuclear membranes, and homogenization of the chromatin, thus creating featureless, dark nuclei. In severely affected chips, coagulation necrosis is present, including tissue devitalization with loss of cell membranes and indistinct smeared chromatin.

Delayed fixation and air drying commonly result in separation of the epithelium and the underlying basement membrane, as well as chromatin smearing and smudging ( Fig. 8.11 ). This artifactual change is more prominent in malignant than benign acini. Cell clusters floating in empty lumina may be mistaken for microvascular invasion.

Degenerating lymphocytes and stromal myocytes may show vacuolization that mimics signet ring cell carcinoma. In difficult cases immunohistochemical stains are useful, with immunoreactivity for leukocyte common antigen in lymphocytes and smooth muscle actin in myocytes; both are negative for keratin AE1/AE3, PSA, and prostatic acid phosphatase (PAP).

Nonprostatic Tissues in Biopsies

Seminal Vesicle and Ejaculatory Duct Tissue in Biopsies

Up to 20% of prostate biopsy specimens contain fragments of seminal vesicle or ejaculatory duct epithelium, potential sources of diagnostic confusion. The mucosa displays complex papillary folds and irregular convoluted lumina, and the lining consists of a nonciliated pseudostratified tall columnar epithelium. The cells are predominantly secretory, with microvesicular lipid droplets and characteristic age-related refractile golden-brown lipofuscin pigment granules; cytologic atypia is the norm ( Figs. 8.12 and 8.13 ). The muscular wall consists of a thick circumferential coat of smooth muscle.

Cowper Gland Tissue in Biopsies

Cowper glands are small paired bulbomembranous urethral glands that may be mistaken for prostatic carcinoma in biopsies. These glands are composed of lobules of closely packed uniform acini lined by cytologically benign cells with abundant apical mucinous cytoplasm ( Fig. 8.14 ). Nuclei are small, solitary, punctate, and basally located, and nucleoli are inconspicuous. Cowper glands are embedded in smooth muscle, thus mimicking the infiltrative pattern of prostatic cancer. Misdiagnosis can be avoided when samples display immunoreactivity for mucin and smooth muscle actin, and are negative for PSA and PAP.

Disorders of Cowper glands are exceedingly rare. Urethral syringocele is cystic dilatation that may cause voiding dysfunction in children and is not apparently associated with other congenital anomalies. A single case of giant cystadenoma occurred in a 41-year-old man who presented with acute obstruction. Carcinoma is exceedingly rare and is characterized by frank anaplasia of tumor cells.

Secretory Luminal Cells

The secretory luminal cells are cuboidal to columnar, with small, round nuclei, punctate or inconspicuous nucleoli, finely granular chromatin, and pale to clear cytoplasm; they account for the bulk (73%) of the epithelium volume. Despite having the lowest proliferative activity, the terminally differentiated secretory cells produce PSA, PAP, androgen receptors, acidic mucin, and other secretory products. They also express high levels of keratins 8 and 18, but lack keratins 5 and 14, as well as p63.

Basal Cells

The basal cells of the prostate form a flattened, attenuated layer of inconspicuous elongate cells at the periphery of the glands surmounting the basement membrane ( Fig. 8.15 ). These cells possess the highest proliferative activity of the epithelium, albeit low, and a subset is thought to act as stem or “reserve” cells that repopulate the secretory cell layer. Basal cells retain the ability to undergo metaplasia, including squamous differentiation in the setting of infarction and myoepithelial differentiation in sclerosing adenosis. Epidermal growth factor receptors have been identified in basal cells, but not in secretory cells, a finding suggesting that these cells play a role in growth regulation. Basal cells are selectively labeled with antibodies to high-molecular-weight keratins such as clone 34βE12, a property that is exploited immunohistochemically in separating benign acinar processes such as atrophy, which retains a basal cell layer, from cancer, which lacks a basal cell layer. The nuclear protein p63 is another diagnostically useful basal cell marker that consistently decorates nuclei. Basal cell–specific immunohistochemical cocktail (the combination of cytoplasmic antikeratin 34βE12 and nuclear antip63) optimizes the sensitivity of basal cell detection compared with either stain alone. Basal cells also express high levels of keratins 5 and 14, in contrast with secretory and intermediate cells, as well as bcl-2, glutathione S-transferase pi, and galactin 3. Basal cells contain little or no PSA, PAP, androgen receptors, keratins 8 or 18, or mucin. The normal prostatic epithelium frequently displays focal basal cell proliferation that is too small to warrant the diagnosis of basal cell hyperplasia. Prostatic basal cells do not normally possess myoepithelial differentiation, unlike basal cells in the breast, salivary glands, pancreas, and other sites, probably because the massive smooth muscle stroma of the prostate propels secretions downstream without need for assistance from basal cells. The basal cell population is heterogeneous in its expression of different combinations of p63, keratin 5, and keratin 14 differentiation markers, and the p63 ⁺ /K5 ⁻ /K14 ⁻ subpopulation is proposed as likely stem cells.

Neuroendocrine Cells

Neuroendocrine cells are the least common cell type of the prostatic epithelium, and they are usually not identified in routine H&E-stained sections except for rare cells with large eosinophilic granules. Although their function is unknown, neuroendocrine cells probably have an endocrine-paracrine regulatory role in growth and development, similar to neuroendocrine cells in other organs, and contain numerous neuropeptides that modulate cell growth and proliferation. Androgen deprivation therapy does not appear to influence the number or distribution of neuroendocrine cells in the normal or neoplastic prostate. These cells coexpress PSA and androgen receptors, a finding suggesting a common cell of origin for epithelial cells and neuroendocrine cells in the prostate. Neural crest origin has been shown for at least a subset of these cells.

Recognition that neuroendocrine cells are most numerous near the verumontanum suggests a role in luminal constriction and dilatation. Serotonin and chromogranin are the best immunohistochemical markers in formalin-fixed sections ( Figs. 8.16 and 8.17 ). African American men have low neuroendocrine cell expression compared with other ethnic groups, and this may play a role in their increased risk for cancer.

Three patterns of neuroendocrine differentiation are seen in human prostatic carcinoma: (1) infrequent small cell neuroendocrine carcinoma, (2) rare carcinoid-like cancer, and (3) conventional prostatic cancer with focal neuroendocrine differentiation (see Chapter 9 ). Virtually all cases of prostatic adenocarcinoma contain at least a small number of neuroendocrine cells, but special studies such as histochemistry and immunohistochemistry are usually necessary to identify these cells. Neuroendocrine differentiation typically consists of scattered cells that are inapparent by light microscopy but revealed by immunoreactivity for one or more markers. Neuroendocrine cells in prostate cancer are malignant and lack androgen receptor expression. These cells have no apparent clinical or prognostic significance in benign epithelium, primary prostatic adenocarcinoma, and lymph node metastases, according to most but not all reports.

Stem Cells

Stem cell–derived clonal units found in the normal, atrophic, hyperplastic, and dysplastic epithelium actively replenish the entire epithelium during aging. These deficient areas usually include the basal compartment, a finding indicating the location of stem cells. CD133 has been successfully used as a stem cell marker in both benign and malignant prostate. CD24 is a marker expressed on the basal transit-amplifying cells (transition cells) and may play a role in the differentiation and migration of basal stem cells to the luminal layer. Androgen receptors appear to play a significant regulatory role in maintaining the balance between progenitor basal cells and luminal secretory cells. Androgen receptors are expressed at a low level in basal cells, but they play a suppressive role in the proliferation of the CK5 ⁺ /CK8 ⁺ progenitor/intermediate cells and a positive (proliferative) role in the CK5 ⁻ /CK8 ⁺ luminal epithelial cells.

Luminal Products

Intraluminal products of benign prostatic acini may include mucin, degenerating epithelium, crystalloids, proteinaceous debris, prostasomes, corpora amylacea, calculi, and spermatozoa.

Prostatic secretions are composed chiefly of simple sugars and are mildly alkaline. The protein content is less than 1%, including proteolytic enzymes, PSA, PAP, β-microseminoprotein, and abundant zinc. In an animal model, luminal secretions increased significantly in the presence of inflammation. Proteinaceous secretions are a frequent nonspecific finding in benign and neoplastic acini (overall 8% incidence rate in one study, with 100% incidence rate in men > 70 years of age), and are considered the precursors of corpora amylacea and calculi. Dilated acini with thyroid-like secretions are rarely observed in the prostate ( Fig. 8.18 ), reminiscent of the luminal products seen in thyroidization of renal tubules and thyroid-like follicular carcinoma of the kidney; we refer to this as thyroidization of prostatic acini.

Mucin is usually absent in benign acini. Histochemical staining demonstrates neutral mucins (periodic acid–Schiff [PAS] with diastase), whereas neoplastic acini often demonstrate neutral and acidic mucins (Alcian blue–positive [pH 2.5]). However, acidic mucin is not specific for cancer because certain benign conditions may also express it, including mucinous metaplasia, sclerosing adenosis, atypical adenomatous hyperplasia (AAH), and high-grade PIN. Mucins MUC1, MUC2, MUC4, MUC5AC, and MUC6 are not found in benign epithelium, although conflicting results have been found with MUC1 and MUC4. Positive staining for MUC6 in seminal vesicle epithelium may be useful for excluding prostatic origin.

It should be noted that mucin can also be found in the stroma, and raises the following considerations: benign extravasated mucin of unknown origin, stromal Teflon (polytetrafluoroethylene) mimicking mucin ( Fig. 8.19 ; see later), and mucinous adenocarcinoma, in which at least a few cancer cells are invariably found floating in extravasated mucin after careful study.

Corpora amylacea are luminal secretions present in up to 78% of benign acini, but they are observed only rarely in stromal smooth muscle cells and adenocarcinoma (0.4% of needle biopsies with cancer) ( Figs. 8.20 and 8.21 ). They vary in size and shape, but most are round ( Fig. 8.22 ). Color ranges from pink-purple to orange, and the presence of concentric laminations and early mineralization is variable. Corpora amylacea result from stasis of prostatic fluid and desquamated epithelial cells, which may further induce deposition of calcium salts leading to calculus formation, possibly generating a cycle of further irritation, additional blockage, and greater inflammation and mineralization.

Ultrastructurally corpora amylacea are composed of bundles of fibrils and occasional interspersed electron-dense areas. Biochemical analysis and x-ray diffraction reveals that the main constituent is sulfated glycosaminoglycans ; other components include lactoferrin, calprotectin, myeloperoxidase, and α-defensins, proteins contained in neutrophil granules, thus suggesting a pathogenic role for acute inflammation.

Prostasomes are prostate-derived membranous vesicles that can be isolated from seminal plasma. They have been proposed to perform a variety of functions, including modulation of (immune) cell activity within the female reproductive tract and stimulation of sperm motility and capacitation.

Calculi (microcalcifications), present in 31% to 100% of prostates, are typically found in central large ducts ( Fig. 8.23 ), and are composed predominantly of calcium phosphate in the form of hydroxyapatite. One study found calcifications in 89% of prostates, 58% of seminal vesicles, and 17% of ejaculatory ducts. Calcifications occur mainly in benign glands and/or stroma of all zones and the verumontanum, but are most common in the transition zone, often observed in association with inflammation, BPH, and basal cell hyperplasia. Whereas luminal microcalcifications are commonly observed in breast cancer, prostatic calculi are rarely seen in malignant acini. Interestingly, stromal microcalcifications are observed in approximately 3% of needle biopsy specimens, invariably in association with chronic inflammation. Gross prostatic calcification, occupying an area of more than 3 cm ² on a standard x-ray, is rare.

Calcifications are more prevalent in autopsy prostates from African Americans in Washington, DC, than from Africans from West Africa, a finding perhaps reflecting dietary differences. There is a positive correlation of prostatic calcification and age. Calcification is also common in patients with chronic pelvic pain syndrome and is associated with inflammation, bacterial colonization, and symptom duration. Calcific deposits of Mönckeberg medial calcinosis are occasionally observed in arteries and large arterioles in the periprostatic tissue.

Intraprostatic spermatozoa can be identified with Berg stain, present in 26% of prostates at radical prostatectomy, including the peripheral zone (72%), central zone (22%), and transition zone (6%). They are frequently associated with inflammation and atrophy, including postatrophic hyperplasia (PAH).

Pigment

Pigment is occasionally observed in the cytoplasm of the secretory epithelium, including lipofuscin and melanin. Lipofuscin granules are golden-brown, gray-brown, or blue by H&E staining ( Fig. 8.24 ), display autofluorescence, and are positive for Fontana-Masson, PAS with diastase, Congo red, Luxol fast blue, and oil red O stains. Similar pigment may be also found in seminal vesicle and ejaculatory duct epithelium, high-grade PIN, and adenocarcinoma. One should avoid misinterpretation of pigmented acini adjacent to carcinoma as evidence of seminal vesicle invasion on needle biopsy. This pigment represents “wear and tear” or “old age” pigment resulting from endogenous cellular by-products. It is present in all zones and is randomly distributed. Less commonly, melanin-like (Fontana-Masson–positive) pigment is found in scattered foci in the normal and hyperplastic epithelium and stroma ( Fig. 8.25 ) (see later Melanosis section).

Immunohistochemistry

The most important immunohistochemical markers in prostate pathology are PSA, PAP, high-molecular-weight keratin 34βE12, p63, racemase (P504S), c-myc, NKX3.1, and ERG. Androgen receptor immunostaining has not been used in routine clinical work because of variable results in multiple studies. Standardization of methods of staining and quantitation for all stains is recommended to avoid variable results. These markers are briefly presented here, but they are discussed at length in Chapter 9 .

Prostate-Specific Antigen

Immunohistochemical expression of PSA (human glandular kallikrein 3 [hK3]) is useful for distinguishing prostate cancer, especially high-grade cancer, and urothelial carcinoma, colonic carcinoma, granulomatous prostatitis, and lymphoma. PSA also facilitates identification of site of tumor origin in metastatic adenocarcinoma. Table 8.4 lists extraprostatic tissues and tumors that express PSA immunoreactivity.

PSA can be detected in frozen sections, paraffin-embedded sections, cell smears, and cytologic preparations of normal and neoplastic epithelium ( Fig. 8.26 ). In the normal and hyperplastic prostate, PSA is uniformly present at the apical portion of the glandular epithelium of secretory cells. The intensity of the staining decreases in poorly differentiated adenocarcinoma. Staining is invariably heterogeneous. Microwave antigen retrieval is usually not necessary, even in tissues that have been immersed in formalin for years. Formalin fixation is optimal for localization of PSA, and variation in staining intensity is only partially the result of fixation and embedding effects. Immunoreactivity is preserved in decalcified specimens and may instead be enhanced.

p63

p63 is the stain of choice for nuclear staining of basal cells and is an excellent complement to high-molecular-weight cytokeratin staining of the cytoplasm ( Fig. 8.27 ). p63 may be more sensitive than 34βE12 in staining benign basal cells, particularly in TURP specimens, and it may offer advantages over 34βE12 in diagnostically challenging cases. The immunohistochemical cocktail (34βE12 and p63) increased the sensitivity of basal cell detection and reduced staining variability. The p63 gene is also expressed in respiratory epithelia, breast and bronchial myoepithelial cells, cytotrophoblast cells of human placenta, scattered cells of lymph nodes and germinal centers, and squamous cell carcinoma of the lung. Quadruple staining with high-molecular-weight cytokeratin, p63, racemase, and c-myc is used by many laboratories for the diagnosis of prostate cancer.

ERG

TMPRSS2-ERG, the most common gene fusion in prostate cancer, is associated with expression of a truncated protein product of the oncogene ERG. A novel anti-ERG monoclonal antibody has been characterized, and immunohistochemical ERG expression is highly concordant with the ERG mRNA overexpression (sensitivity, 100%; specificity, 85%). ERG overexpression is the result of TMPRSS2-ERG gene fusion in all cases. ERG protein expression is identified in 52% of cases of high-grade PIN and in 61% of adenocarcinomas on needle biopsies; conversely, only 6% of benign acini adjacent to cancer display weak staining in the secretory cells ( Fig. 8.28 ). No ERG expression is detected in nonprostatic carcinoma, atrophy, and benign and treated tissues of the prostate and seminal vesicles.

Prostate-Specific Membrane Antigen

Prostate-specific membrane antigen (PSMA) is a membrane-bound antigen that is highly specific for benign and malignant prostatic epithelium, although endothelial cells in multiple organs are also immunoreactive. Cytoplasmic epithelial immunoreactivity for PSMA is intense. The number of immunoreactive cells increases from benign epithelium to high-grade PIN and prostatic adenocarcinoma. The most extensive and intense staining for PSMA is observed in high-grade carcinoma, with immunoreactivity in virtually every cell in Gleason primary pattern 4 or 5 ( Table 8.7 ). Extraprostatic expression of PSMA is highly restricted other than for vascular staining, and nonprostatic cancer is invariably negative for PSMA, including renal cell carcinoma, urothelial carcinoma, and colonic adenocarcinoma. PSMA immunoreactivity in cancer cells was not predictive of PSA biochemical failure or recurrence in a cohort of organ-confined margin-negative cancers treated by surgery; these findings differ from serum studies in which elevated concentrations of PSMA indicated surgical treatment failure. PSMA is expressed in lymph node and bone marrow metastases of prostate cancer ( Fig. 8.29 ), thus underscoring its utility in identifying cancer of an unknown primary site. Serum PSMA is of prognostic significance, especially in the presence of metastases, and correlates well with stage in a screened population. Despite its potential utility, PSMA immunohistochemistry is infrequently used in routine practice.

Table 8.7

Comparative Immunoreactivity of Prostate-Specific Membrane Antigen and Prostate-Specific Antigen in the Benign and Neoplastic Prostate in 184 Radical Prostatectomies

	% of Immunoreactive Cells + SD (Range)
Prostate-specific membrane antigen
Benign	69.5 + 17.3 (20-90)
High-grade PIN	77.9 + 13.7 (30-100)
Cancer	80.2 + 13.7 (30-100)
Prostate-specific antigen
Benign	81.3 + 11.8 (20-90)
High-grade PIN	64.8 + 17.3 (10-90)
Cancer	74.2 + 16.2 (10-90)

PIN , Prostatic intraepithelial neoplasia.

Prostatic Immune Response

The immune response in the prostate is primarily cell mediated. Lymphocytes are more numerous in the stroma, and T cells represent more than 90% of the total number of lymphocytes present in both stromal and intraepithelial compartments. Stromal T cells are mainly helper/inducer, whereas intraepithelial T cells are mainly cytotoxic/suppressor cells. This inverted CD4/CD8 ratio in the intraepithelial compartment indicates that cytotoxic/suppressor T cells may represent the first line of defense against luminal foreign agents reaching the prostate through the urethra by retrograde flow. No significant difference exists in the number of lymphocytes (either T or B cells, stromal or intraepithelial) according to the patient age, race, or anatomic zone. These findings indicate that the regulation of lymphocyte function and distribution is tightly controlled, and that there is a constant level of immunosurveillance in the prostate from birth. Increased CD4 ⁺ T-lymphocyte infiltration within cancer is stage independent and associated with poor outcome.

Acute Bacterial Prostatitis

Men at high risk for acute prostatitis include those with diabetes, cirrhosis, and suppressed immune systems. The cause is usually an ascending infection, but bacteria can also be introduced during transrectal biopsy. The prevalence of fluoroquinolone-resistant Escherichia coli acute prostatitis was 13% after biopsy in one study. Biopsy-associated acute prostatitis patients are older, have larger prostate volumes, have higher serum PSA concentrations, and show a higher incidence of septicemia and antibiotic-resistant bacteria than those with spontaneous acute prostatitis.

Patients with acute bacterial prostatitis present with sudden onset of fever, chills, irritative voiding symptoms, and pain in the lower back, rectum, and perineum. The prostate is swollen, firm, tender, and warm. Microscopically, acute inflammation in the prostate is often intraluminal, with a few scattered neutrophils or aggregates. There are sheets of neutrophils surrounding acini, often with marked tissue destruction and cellular debris ( Fig. 8.30 ). The stroma is edematous and hemorrhagic, and microabscesses may be present. Diagnosis is based on culture of urine and expressed prostatic secretions; biopsy is contraindicated because of the potential for sepsis. Most cases are caused by bacteria responsible for other urinary tract infections, including Escherichia coli (80% of infections), other Enterobacteriaceae (5% to 10%), and Pseudomonas , Serratia , and Klebsiella (10% to 15%). Gonococcal prostatitis caused by Neisseria gonorrhoeae was common in the preantibiotic era, but it is less common today. Most cases of acute prostatitis respond to antibiotics, although about 10% eventually progress to chronic bacterial prostatitis and another 10% to chronic pelvic pain syndrome.

Abscess is a rare complication, usually occurring in immunocompromised patients such as those with AIDS. Transrectal ultrasonography is a valuable method for preoperative diagnosis. Many patients with abscesses are treated by TURP and broad-spectrum antibiotics.

Chronic Prostatitis

Chronic bacterial prostatitis is a common cause of relapsing urinary tract infection, and it is often the result of E. coli. Lifetime prevalence rate is 2% to 8%. Clinical diagnosis is difficult, often requiring multiple urine cultures obtained after prostatic massage. Treatment is vexing because of the inability of most intravenous antibiotics to enter the prostate and prostatic fluids when the organ is overrun with a chronic inflammatory infiltrate ( Fig. 8.31 ). Prostatic calculi contain bacteria embedded in the mineral matrix, and this may serve as a nidus of recurrent infection. The secretory products of the inflamed prostate are alkaline, with low levels of zinc, citric acid, spermine, cholesterol, antibacterial factors, and certain enzymes.

Chronic abacterial prostatitis is more common than bacterial prostatitis, and it rarely follows infection elsewhere in the urinary tract. Patients often report painful ejaculation. Results of cultures of urine and expressed prostatic secretions are, by definition, negative. This form of prostatitis has a prolonged indolent course with relapses and remissions.

The causative agent is unknown, but Chlamydia , Ureaplasma , and Trichomonas have been proposed. Early studies using molecular techniques that do not rely on cultures, including molecular-phylogenetic approaches based on 16S RNA techniques, provided disparate results regarding the contributions of bacterial agents. In patients with nodular hyperplasia and prostatitis, Trichomonas vaginalis DNA and antigen were detected in prostate tissue in 25% and 22% of patients, respectively.

No relationship appears to exist between chronic prostatitis and the pathogenesis of BPH. Microscopically, several patterns of chronic inflammation have been described including segregated glandular inflammation, periglandular inflammation, diffuse stromal inflammation, intraepithelial lymphocytes, isolated stromal lymphoid nodules, and single scattered lymphocytes ( Fig. 8.31 ). Total prostatic volume and the aggressiveness of glandular inflammation correlated significantly with serum PSA level in men with nodular hyperplasia. Interstitial infiltration involving T and B lymphocytes with fewer macrophages is a constant finding in early myxoid nodules.

Chronic prostatic inflammation may be classified according to location, extent, and grade ( Table 8.9 ). If more than one grade of inflammation is present for a given anatomic location, the dominant grade and most severe grade are specified (e.g., multifocal mild acinar inflammation, focal mild periacinar inflammation, diffuse mild stromal inflammation, and focal severe stromal inflammation).