• Rare tumor of deep soft tissue characterized by well defined nests of cells separated by fibrous stroma
• 0.5-1.0% of all soft tissue tumors
• Deep soft tissue of oral cavity, pharynx, mediastinum, thigh/leg
• Usually young females
• Highly malignant, although clinical course is slow/indolent
• Metastases up to 30 years later to veins, lungs, other
• Lung metastases may be presenting feature

• Size, presence of 17q25 abnormality, AJCC stage, age

• 5 year old boy with orbital tumor (Afr J Paediatr Surg 2011;8:82)
• 18 year old woman with primary alveolar soft part sarcoma of tongue and CNS metastases (Case of the Week #222)
• 25 year old man with tumor of tongue (Indian J Pathol Microbiol 2011;54:581)
• 44 year old man with metastatic nodule on nose (Indian J Dermatol Venereol Leprol 2012;78:666)

Orbital tumor

Tongue

Nose and thigh

• Well circumscribed, large, gray-yellow, hemorrhage, necrosis
• Size ranges from 2-14 cm

Deep soft tissue

• Well defined nests of cells separated by fibrous stroma
• Alveolar pattern if cells discohesive
• Composed of large polygonal cells with granular eosinophilic cytoplasm, vesicular nuclei, prominent nucleoli
• Vascular invasion common; also characteristic rod-shaped crystalloids
• No/rare mitotic figures, minimal pleomorphism

Various images

Tongue

Lobular structure

Thigh mass

Tongue tumor

Case of the Week #222:

MyoD1

PAS-D

TFE3

Vimentin

• Strong similarity to renal cell carcinoma, clear cell type
• Variably cellular smears composed of large cells with an abundant finely granular or vacuolated cytoplasm, markedly enlarged nuclei/nucleoli, and bare nuclei (Cancer 2009;117:500)

Figures 1-6

Metastatic renal cell carcinoma

• PAS+ diastase resistant needle-like structures, MyoD1 (cytoplasmic only)

• Membrane-bound crystals with periodicity of 58-100 nm and cross grid pattern
• Numerous electron dense vesicles near Golgi
• Smooth tubular aggregates associated with plasmalemmal invaginations
• No features of skeletal muscle differentiation

• Changes in #1, 5, 13, 17

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