Miscellaneous Tumors of Uncertain Differentiation


Benign tumors

Superficial Angiomyxoma

Definition

  • An uncommon distinct type of myxoma characterized by the presence of thin-walled blood vessels

  • This is likely to represent the same entity as cutaneous myxoma, including the lesions seen in Carney complex

Clinical features

Epidemiology

  • Presents during adulthood and shows slight male predilection

  • Commonly affects the head and neck and trunk areas

Presentation

  • Usually solitary

  • Size: 1 to 5 cm

Prognosis and treatment

  • Benign tumors, but frequently recur locally

  • No reports of metastasis

Pathology

Histology

  • Dermal or subcutaneous lobules of plump, stellate or spindle-shaped, bland-looking cells embedded in basophilic, highly vascular, myxoid matrix

  • Aggregates of inflammatory cells, particularly neutrophils, are commom

  • May contain entrapped epithelial component that resembles keratinous cysts

  • Some consider this equivalent to cutaneous myoma

Immunohistochemistry/special stains

  • Neoplastic cells express vimentin and sometimes CD68, factor XIIIa, and CD34

  • The myxoid stroma can be highlighted with Alcian blue or mucicarmine stains

Main differential diagnoses

  • Aggressive angiomyxoma

  • Angiomyofibroblastoma

  • Low-grade myxofibrosarcoma

  • Nerve sheath myxoma

Fig. 1, Superficial angiomyxoma.

Fig. 2, Superficial angiomyxoma.

Fig. 3, Superficial angiomyxoma.

Fig. 4, Superficial angiomyxoma.

Fig. 5, Superficial angiomyxoma,

Intramuscular Myxoma

Definition

  • Benign mesenchymal tumor composed of bland, spindle-shaped cells embedded in a characteristically hypovascular myxoid stroma

Clinical features

Epidemiology

  • An exclusively intramuscular neoplasm

  • It usually involves the large skeletal muscles of extremities, particularly the thigh

  • Superficial cases involving head and neck and hypothenar area of the hand are extremely rare

  • Majority of patients are adults

  • Two-thirds of patients are females

  • Rare cases are associated with Mazabraud syndrome (single or multiple intramuscular myxomas and polyostotic fibrous dysplasia)

Presentation

  • Most cases present as slowly growing, painless muscular masses

  • Angiographic studies demonstrate poorly vascularized neoplasms

Prognosis and treatment

  • Surgical excision is virtually always curative

  • Recurrence is unusual even after incomplete resection

  • Cellular variant has a higher tendency for recurrence

Pathology

Histology

  • Classically described as “hypocellular” and “hypovascular” tumor

  • Commonly infiltrates adjacent muscle fibers

  • Abundant myxoid stroma with sparse, capillary-sized blood vessels

  • Uniform, cytologically bland, spindle-shaped cells with eosinophilic cytoplasm

  • A cellular variant has been described

  • Tumors typically lack cytological atypia, mitoses, and necrosis

Immunhistochemistry/special stains

  • Neoplastic cells express vimentin

  • Variable expression with CD34, desmin, and smooth muscle actin

  • S100 protein is not normally expressed

Genetic profile

  • Recurrent point mutations involving the GNAS1 gene are common

Main differential diagnoses

  • Chondrosarcoma

  • Low-grade myxofibrosarcoma

  • Low-grade fibromyxoid sarcoma

  • Myxoid liposarcoma

  • Myxoid neurothekoma

Fig. 1, Intramuscular myxoma.

Fig. 2, Intramuscular myxoma.

Fig. 3, Intramuscular myxoma.

Fig. 4, Intramuscular myxoma.

Fig. 5, Intramuscular myxoma.

Fig. 6, Intramuscular myxoma.

Juxtaarticular Myxoma

Definition

  • A rare, benign mesenchymal tumor that histologically resembles intramuscular myxoma and usually arises in the vicinity of a joint

Clinical features

Epidemiology

  • Wide age range

  • The majority of affected individuals are males (more than 70%) in their third to fifth decades

  • The most common location is around the knee

  • Mainly involves the periarticular tendons, ligaments, joint capsule, muscles, and the adjacent subcutis

Presentation

  • Most cases present as a mass, sometimes associated with pain

Prognosis and treatment

  • Benign tumors often cured by complete excision

  • Recurrence is common; can be multiple

  • Recurrence usually takes place within 18 months

  • Recurrence commonly involves subcutaneous adipose tissue

Pathology

Histology

  • Histologically virtually identical to intramuscular myxoma

  • Unlike intramuscular myxoma, cystic changes are more common, and rare mitoses as well as atypical reactive cells can be seen

Immunohistochemistry/special stains

  • Alcian blue–positive matrix

  • Neoplastic cells express vimentin

  • Variable expression with CD34, desmin, and smooth muscle actin

  • S100 protein is not normally expressed

Genetic profile

  • Recurrent point mutations involving the GNAS1 gene are not seen

Main differential diagnoses

  • Ganglion cyst

  • Chondrosarcoma

  • Low-grade myxofibrosarcoma

  • Low-grade fibromyxoid sarcoma

  • Myxoid liposarcoma

  • Myxoid neurothekoma

Fig. 1, Juxtaarticular myxoma.

Fig. 2, Juxtaarticular myxoma.

Fig. 3, Juxtaarticular myxoma.

Fig. 4, Juxtaarticular myxoma.

Ectopic Hamartomatous Thymoma

Definition

  • A rare, suprasternal, heterogeneous tumor composed of an admixture of spindle cells, epithelial cells, and adipose tissue with a presumed branchial origin

  • Despite the name, there is no definite evidence of thymic origin or thymic differentiation

  • The designation branchial anlage mixed tumor has been proposed to describe this entity

Clinical features

Epidemiology

  • Majority of patients are adults

  • Striking male predominance

Presentation

  • Slowly growing, small, lower neck mass

Prognosis and treatment

  • Generally benign lesion

  • Cured by complete resection

  • No reports of metastasis

Pathology

Histology

  • Tumors consist of three haphazardly arranged components: epithelial cell, spindle cell, and adipose tissue

  • Spindle cell component usually predominates

  • The epithelial component consists of either solid or cystic squamous epithelium

  • Glandular structures are less common

  • The spindle cells exhibit bland-looking elongated nuclei

  • Myoid differentiation of spindle cells is sometimes seen

  • Myoepithelial differentiation is uncommon

  • Tumor cells are devoid of pleomorphism

  • Mitoses are usually absent

  • Scattered lymphocytes may be seen

Immunohistochemistry/special stains

  • Both epithelial and spindle cells express cytokeratins, particularly high-molecular-weight forms

  • CD34 is expressed by the spindle cells only

  • Androgen receptor is expressed by the spindle cells

  • Muscle actin and myoglobin can be expressed by spindle cells

  • Desmin and S100 protein are negative

Main differential diagnoses

  • Ectopic cervical thymoma

  • Thymolipoma

  • Teratoma

  • Biphasic synovial sarcoma

  • Malignant peripheral nerve sheath tumor with glandular differentiation

  • Benign mixed tumor/myoepithelioma of soft tissue

Fig. 1, Ectopic hamartomatous thymoma.

Fig. 2, Ectopic hamartomatous thymoma.

Fig. 3, Ectopic hamartomatous thymoma.

Fig. 4, Ectopic hamartomatous thymoma.

Intermediate tumors

Hemosiderotic Fibrolipomatous Tumor

Definition

  • Also known as hemosiderotic fibrohistiocytic lipomatous lesion

  • A rare, superficial proliferation composed of spindle cells and adipocytes that almost exclusively involves the ankle

  • An association between myxoinflammatory fibroblastic sarcoma and hemosiderotic fibrolipomatous tumor reported recently, as both lesions can share an identical translocation at t(1;10)(p22;q24)

Clinical features

Epidemiology

  • Affected individuals are usually adults

  • Predilection for females

Presentation

  • Slowly growing, may be painful

  • Size is variable

  • History of trauma is obtained in up to 70% of cases

Prognosis and treatment

  • Treated by local excision

  • Local recurrence can occur

  • No reports of metastasis

Pathology

Histology

  • Well-circumscribed lobules of mature adipocytes admixed with areas composed of spindle cells

  • The spindle cell areas show striking hemosiderin deposition

  • No or mild atypia

  • No or rare mitoses

  • Sometimes associated with venous stasis and can be histologically virtually identical to early pleomorphic, hyalinizing angiectatic tumor (but is not pathogenically related to this tumor)

  • Hybrid lesions with myxoinflammatory fibroblastic sarcoma can be encountered (the two tumors do appear to be pathogenically related in at least a subset of cases)

Immunohistochemistry/special stains

  • The spindle cells express vimentin, CD34, and calponin

Genetic profile

  • Distinctive translocation t(1;10)(p22;q24) involving the TGFBR3 and MGEA5 genes in the great majority of cases, frequently also associated with amplifications of chromosome 3p11~12, resulting in formation of ring chromosomes (also designated marker chromosomes ) with increased expression of VGLL3 and CHMP2B genes

  • Myxoinflammatory fibroblastic sarcoma can harbor this fusion in a subset of cases

  • TGFBR3-MGEA5 fusions are more commonly encountered in hybrid hemosiderotic fibrolipomatous tumor/myxoinflammatory fibroblastic sarcoma lesions than in classical “pure” myxoinflammatory fibroblastic sarcomas

  • These features suggest a pathogenical relationship between at least a subset of these two tumor types

Main differential diagnoses

  • Spindle cell lipoma

  • Atypical lipomatous tumor

Fig. 1, Hemosiderotic fibrolipomatous tumor.

Fig. 2, Hemosiderotic fibrolipomatous tumor.

Fig. 3, Hemosiderotic fibrolipomatous tumor.

Fig. 4, Hemosiderotic fibrolipomatous tumor.

Fig. 5, Hemosiderotic fibrolipomatous tumor.

Fig. 6, Hemosiderotic fibrolipomatous tumor.

Fig. 7, Hemosiderotic fibrolipomatous tumor.

Deep (Aggressive) Angiomyxoma

Definition

  • A mesenchymal neoplasm composed of stellate or spindle cells that commonly exhibit myoid differentiation embedded in an abundant myxedematous stroma

Clinical features

Epidemiology

  • Affected patients are almost exclusively females 40 to 60 years of age

  • Much less common in women older than 60 years and does not affect children

  • Tumors are usually deeply located in pelvic, perineal, anorectal, or retroperitoneal regions

Presentation

  • Commonly present as asymptomatic, slowly growing mass

  • Patients may present with feeling of pressure, discomfort, or pain

  • Size is variable but often large (>10 cm)

Prognosis and treatment

  • Locally aggressive tumors (intermediate)

  • Recurrence is common, which can be late, but usually not more than once

  • No metastases have been reported

  • Usually managed by surgical excision

  • May respond to hormonal therapy using gonadotropin-releasing hormone agonist

Pathology

Histology

  • Sparsely to moderately cellular neoplasms composed of bland stellate and spindled cells embedded in a loosely collagenized, myxoid matrix with scattered vessels of varied caliber

  • Higher cellularity may be observed at perivascular and peripheral areas

  • Some neoplastic cells show relatively abundant eosinophilic cytoplasm and exhibit fibroblastic and myofibroblastic features and appear to be hormonally influenced

  • Well-developed myoid differentiation best evident around medium-size blood vessels and nerve trunks

  • Mitoses are rare or absent

Immunohistochemistry/special stains

  • Neoplastic cells focally express desmin, smooth muscle actin, muscle specific actin, vimentin, CD34, and estrogen and progesterone receptors

  • S100 protein is negative and Ki-67 index is very low (<1%)

  • The myxoid stroma can often be highlighted with Alcian blue or mucicarmine stains

Main differential diagnoses

  • Superficial angiomyxoma

  • Angiomyofibroblastoma

  • Low-grade myxofibrosarcoma

  • Nerve sheath myxoma

Fig. 1, Deep angiomyxoma.

Fig. 2, Deep angiomyxoma.

Fig. 3, Deep angiomyxoma.

Fig. 4, Deep angiomyxoma.

Fig. 5, Deep angiomyxoma.

Fig. 6, Deep angiomyxoma.

Fig. 7, Deep angiomyxoma.

Atypical Fibroxanthoma

Definition

  • Distinctive proliferation confined to the dermis by convention and composed of highly atypical, epithelioid histiocyte–like cells and spindled fibroblast-like cells, in variable proportions, occurring on sun-exposed and sun-damaged skin with invariably benign clinical course

  • Diagnosis is one of exclusion and requires additional immunohistochemistry

  • Mutations in TP53 induced by UVA exposure have been implicated in the pathogenesis

Clinical features

Epidemiology

  • Adult patients, most commonly in the eighth decade of life (mean age 77 years)

  • Male predominance (M:F = 9 : 1)

  • Ultraviolet (UV) irradiation a key factor implicated in pathogenesis

Presentation

  • Sun-exposed and sun-damaged skin

  • Most frequently on the scalp, followed by forehead, ear, nose, and face

  • Rapidly growing polypoid or nodular lesion, frequently ulcerated on the surface

Prognosis and treatment

  • Complete excision usually curative

  • Invariably benign when strict criteria applied

  • Virtually always benign when confined to the dermis

  • Locally aggressive behavior and even metastasis can be seen with significant subcuticular involvement (see Pleomorphic dermal sarcoma later)

Pathology

Histology

  • Admixture of (in variable proportions)

    • Pleomorphic, fibroblast-like spindle cells

    • Histiocyte-like epithelioid cells

    • Multinucleated giant cells

  • Lesional cells growing in sheets and fascicles

  • No connection with the epidermis

  • Numerous mitoses, including atypical ones

  • Tumor necrosis absent

  • Lymphovascular invasion absent

  • Perineural invasion absent

  • Generally well-demarcated proliferation in the dermis

  • Focal, limited extension into superficial subcutis not uncommon and allowed by some authorities

    • Expansile

    • Limited lacelike

  • Surface ulceration in about 50% of cases

  • Epidermal collarette at the periphery of the lesion in 20%, possible extension at variable length along the base of the lesion

  • Solar elastosis, usually marked in the surrounding dermis

  • Diagnosis of exclusion

  • Morphological variants (represent either a focal phenomenon or predominant/exclusive component of the lesion)

    • Spindle cell with more limited pleomorphism

      • Proliferation of monomorphic spindle cells

      • No pleomorphism of conventional atypical fibroxanthoma

      • Fascicular growth of spindle cells with eosinophilic cytoplasm

      • High mitotic activity

    • Pseudoangiomatous or “pigmented” variant with hemosiderin deposition

      • Areas of hemorrhage, usually coupled with hemosiderin deposition

      • Pseudovascular spaces lined by lesional cells (pleomorphic spindle cells, epithelioid cells, multinucleated giant cells)

      • Pleomorphic lesional cells can protrude into the pseudolumina

      • Phagocytosis of hemosiderin and erythrocytes occasionally seen

    • Keloidal

      • Bright eosinophilic, hypocellular/acellular, collagenous, keloidlike areas

      • Usually a focal phenomenon

      • Keloidal areas can be separated from the epidermis by a grenz zone

      • Occasionally in a perivascular distribution

    • Regressing

      • Degree of fibrosis from 10% to 90% of the lesion

        • Thickened collagen bundles with sclerosis (early)

        • Lamellar arrangement of collagen fibers with hyalinization (late)

    • Clear cell change

      • Numerous intracytoplasmic lipid vacuoles in lysosome-rich cells

      • Can also represent a degenerative phenomenon

      • Staining for glycogen uniformly negative

    • Granular cell change

      • Bright eosinophilic granular cytoplasm

      • Likely a degenerative phenomenon related to the accumulation of intracytoplasmic lysosomes

    • Myxoid degeneration

      • Accumulation of hyaluronic acid in the stroma

      • Can be highlighted by periodic acid–Schiff (PAS) or Alcian blue

    • Osteoclast-like giant cells

      • Reactive, osteoclast-like giant cells dispersed among conventional atypical fibroxanthoma

      • True atypical osteoclast-like giant cells also described, likely developing from large, pleomorphic, multinucleated giant cells

Immunohistochemistry/special stains

  • Diagnosis of exclusion: must exclude other mimics by immunohistochemistry

  • By definition, consistently negative for low- and high-molecular-weight cytokeratins, desmin, and S100 protein

  • Reactive S100 protein–positive dendritic cells can on occasion be numerous and should not be mistaken for lesional cells

  • Smooth muscle actin positivity (45%), EMA positivity (24%), usually focal

  • CD99 and CD10 frequently positive, but very nonspecific

  • Cytoplasmic CD31 positivity in about 10%

    • Staining is cytoplasmic and finely granular

    • Not as prominent as in endothelial cells

    • Lesional macrophages can also display cytoplasmic positivity

  • Granular cell variant

    • NKIC3 positive

    • PAS positive after diastase digestion

Main differential diagnoses

  • Squamous cell carcinoma

  • Metaplastic carcinoma

  • Melanoma

  • Angiosarcoma

  • Leiomyosarcoma

  • Undifferentiated (dermal) pleomorphic sarcoma

Fig. 1, Atypical fibroxanthoma.

Fig. 2, Atypical fibroxanthoma.

Fig. 3, Atypical fibroxanthoma.

Fig. 4, Atypical fibroxanthoma.

Fig. 5, Atypical fibroxanthoma.

Fig. 6, Atypical fibroxanthoma.

Fig. 7, Atypical fibroxanthoma.

Fig. 8, Atypical fibroxanthoma.

Fig. 9, Atypical fibroxanthoma.

Fig. 10, Atypical fibroxanthoma.

Fig. 11, Atypical fibroxanthoma with clear cell change

Fig. 12, Atypical fibroxanthoma with granular cell change.

Fig. 13, Atypical fibroxanthoma with keloidal areas.

Fig. 14, Atypical fibroxanthoma with keloidal areas

Fig. 15, Atypical fibroxanthoma

Fig. 16, Atypical fibroxanthoma

Fig. 17, Atypical fibroxanthoma

Fig. 18, Atypical fibroxanthoma

Angiomatoid Fibrous Histiocytoma

Definition

  • Uncommon variant of fibrohistiocytic tumor characterized by the presence of cystic hemorrhagic spaces

  • Formerly known as angiomatoid malignant fibrous histiocytoma

Clinical features

Epidemiology

  • Affected patients are children or young adults

  • Tumors are usually located in the subcutaneous tissue of extremities or trunk

  • Deeply situated lesions are less commonly encountered

Presentation

  • Superficial, slow growing

  • Size: few millimeters to 2 cm

  • May be associated with systemic symptoms (fever, anemia, malaise, and weight loss)

Prognosis and treatment

  • Good outcome achieved with simple surgical excision

  • Local recurrence is reported in 10%

  • Deep lesions elicit higher tendency for recurrence

  • Metastasis to local lymph nodes is seen in only 1% of cases

Pathology

Histology

  • Pseudoencapsulated, multicystic, hemorrhagic lesions

  • Neoplastic elements are bland-looking, round or spindle cells admixed with chronic inflammatory cells

  • Inflammatory infiltrates can organize with germinal centers simulating lymph node metastasis

  • Tumor cells may exhibit mild to moderate pleomorphism and occasional mitoses

Immunohistochemistry/special stains

  • Neoplastic cells commonly express CD68, CD99, muscle actin, desmin, EMA, and calponin

  • No reactivity with factor VIII, CD34, CD31, S100 protein, or cytokeratin

Genetic profile

  • t(12;16)(q13;p11) creating ATF1 - FUS fusion gene, t(12;22)(q13;q12) creating ATF1 - EWSR1 fusion gene, or t(2;22)(q33;q12) creating CREB1 - EWSR1 fusion gene—this latter being the most common

Ultrastructure

  • Cells show variable features, including fibroblastic, myofibroblastic, and histiocytic differentiation

Main differential diagnoses

  • Aneurysmal fibrous histiocytoma

  • Angiosarcoma

Fig. 1, Angiomatoid fibrous histiocytoma.

Fig. 2, Angiomatoid fibrous histiocytoma.

Fig. 3, Angiomatoid fibrous histiocytoma.

Fig. 4, Angiomatoid fibrous histiocytoma.

Fig. 5, Angiomatoid fibrous histiocytoma.

Fig. 6, Angiomatoid fibrous histiocytoma.

Fig. 7, Angiomatoid fibrous histiocytoma.

Myoepithelioma of Soft Tissue

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here