Renal neoplasia

Benign epithelial neoplasms

Papillary adenomas are unencapsulated small (≤15 mm in diameter) papillary epithelial proliferations ( Fig. 10.1 ). They are seen frequently in older patients and in patients with end-stage renal disease (ESRD) undergoing dialysis with acquired cystic disease. Papillary adenomas are also found concurrently with papillary RCC, suggesting that they may be precursors or part of a continuum of progression to malignancy. Papillary lesions greater than 15 mm are classified as papillary renal cell carcinomas, which are often well circumscribed and encapsulated. Of note, the true size and presence of a fibrous capsule of a papillary lesion partially represented in a kidney core biopsy may not be discernible, and absolute classification then cannot be made.

Renal oncocytomas are believed to arise from the intercalated cells of renal collecting tubules. Patients are generally asymptomatic at the time of diagnosis, with their tumors discovered incidentally during investigation of hypertension, hematuria, and/or flank or abdominal pain. These tumors are typically well-circumscribed, mahogany-brown solid tumors of variable size with a central scar commonly present. Microscopically, they are composed predominantly of round to polygonal cells with densely granular eosinophilic cytoplasm, round uniform nuclei with smoothly dispersed chromatin, and a central nucleolus embedded in a hyalinized or myxoid stroma ( Figs. 10.2–10.5 ). Ultrastructurally, tumor cells have basal lamina; rarely, intercellular or cytoplasmic lumina; and apical, short, stubby microvilli. The cytoplasm is closely packed with mitochondria showing lamellar or focally stacked cristae (see Fig. 10.4 ).

Renal cell carcinomas

Approximately 2% of all new cancer cases worldwide originate in the kidney. RCC affects male patients approximately twice as often as female patients. RCC has been linked to acquired cystic kidney disease and ESRD. Although most cases are sporadic, 2% to 4% have a familial cause and are notably prevalent in individuals with von Hippel-Lindau (VHL) disease. RCCs vary widely in size, ranging from 1 to 2 cm to massive tumors weighing several times the weight of the normal kidney. They are usually unilateral and unicentric. Bilaterality and multicentricity are features of hereditary carcinomas. Prognosis is highly variable and depends on subtype, grade, and stage.

RCCs are typically solid, ovulated masses that bulge into the renal parenchyma. Although they may appear circumscribed, they frequently infiltrate the perinephric tissues and invade the vasculature, predominately the venous structures. An orange-yellow coloration is typical of the clear cell type, which often has foci of necrosis and scattered areas of hemorrhage ( Fig. 10.6 ). Chromophilic tumors may give a more friable, crumbling appearance.

Microscopically, RCCs have a great diversity of patterns, as outlined in the 2016 WHO classification, which includes several new entities based on genetic profiles and syndromic associations (see Table 10.1 ). They may be diffuse, tubular, cystic, papillary, or sarcomatoid. Because the kidney is derived from the mesenchyme, the sarcomatoid tumors have features that resemble leiomyosarcomas or fibrosarcomas. The new WHO/International Society of Urologic Pathologists (ISUP) grades are based either on nucleolar prominence (grades 1–3) or the presence of nuclear pleomorphism, tumor giant cells, and/or rhabdoid or sarcomatoid differentiation (grade 4; Table 10.2 ) and are used as prognostic indicators in clear cell and papillary renal cell carcinomas. Ultrastructurally, clear cell RCC contains abundant lipid and glycogen, whereas chromophobe RCC is characterized by the presence of abundant intracytoplasmic vesicles ( Figs. 10.7–10.22 ).

The College of American Pathologists (CAP) has provided standards for the reporting of surgical resections of renal tumors. These standards provide a synopsis of cancer pathology staging and prognostic and predictive parameters ( Tables 10.3–10.5 ). The standards can be accessed on the organization’s website (CAP.org). They include macroscopic and microscopic grading and staging in a standard format. They also include a specific section describing the pathology of the nonneoplastic kidney that should identify evidence of medical renal disease involvement. Glomerular, tubulointerstitial, and vascular changes should be described and interpreted.