• Uncommon, usually mass in deep soft tissues of distal extremities of young adults, often hand, M/F = 2:1 (Stanford University)
• "Carcinoma of soft tissue," like synovial sarcoma and adamantinoma of soft tissue
• Typically recur, metastases in 45% of cases, usually to lungs, skin (including scalp), lymph nodes
• Poor prognosis; death from disease in 31%
• Frequently underdiagnosed
• May have atypical biological behavior of tumor due to nodal metastases, size, unusual localizations (Rom J Morphol Embryol 2005;46:229, JCAD Online 2009)
• May derive from mesenchymal cells undergoing epithelial differentiation

• Poor prognostic factors: proximal/axial tumor, large size, deep tumor, hemorrhage, mitotic figures, necrosis, rhabdoid features, angiolymphatic invasion

• 33 year old man with tumor arising from perineural sheath of median nerve (Sarcoma 2009;2009:595391)

• Excision, radiation therapy

Foot

• Epithelioid tumor cells in granuloma-like fashion around areas of necrosis and central hyalinization
• Striking acidophilic tissue due to cytoplasmic staining and desmoplasia
• Tumor usually in reticular dermis, sometimes deeper soft tissue around fascial plans, aponeuroses, tendon sheaths

Site unknown

Forearm

Cyclin D1+

keratin+, IN1-

Rhabdoid cells

• Keratin, EMA, vimentin, CD34 (Histopathology 1998;33:425), rarely CD31 (Virchows Arch 2003;443:93), CA-125 (Jpn J Clin Oncol 2004;34:149)

• Factor VIII related antigen (Virchows Arch A Pathol Anat Histopathol 1987;410:309)
• INI1 / hSNF5 / SMARCB1 (86-93%, both proximal and conventional [Am J Clin Pathol 2009;131:222, Am J Surg Pathol 2009;33:542]), S100, FLI-1

• Abundant intermediate filaments, desmosome-like junctions, small intercellular spaces with microvilli

• Usually DNA copy number changes, gains > losses, including +11q13, 1q21-q23, 6p21.3, 9q31-qter, losses at 9pter-p23, 13q22-q32, others (Mod Pathol 2000;13:1092), SMARCB1 deletions (Mod Pathol 2013;26:385)

• Granulomatous inflammation

• Confined to skin or subcutaneous fat, with little/no involvement of deep soft tissues
• 20% have history of prior trauma
• Accurate diagnosis usually established only after repeated biopsies

Foot

Hand

• Ulcerated papule or nodule on distal extremity of young adult

• Pseudogranulomatous pattern, bland cytology
• Monomorphous cell population
• Hyalinized focally calcified stroma
• Mummified remnants of necrotic epithelioid cells present

4A-vimentin, 4B-EMA

Forearm

• Keratin, EMA, vimentin

• FLI1 (Am J Surg Pathol 2001;25:1061)

• Granulomatous inflammation

• First described in 1997 (Am J Surg Pathol 1997;21:130)
• Arises in soft tissue of proximal limbs or trunks
• Frequently with epithelioid features and rhabdoid phenotype
• Worse prognosis than "distal" type (Mod Pathol 2001;14:655)
• May be variant of extrarenal malignant rhabdoid tumor
• Aggressive behavior; metastases frequently lead to death

• 34 year old man with scrotal abscess (Case of the Week #69)
• 47 year old man with perineal soft tissue mass (World J Surg Oncol 2007;5:28)
• 50 year old man with scrotal mass (Eur Urol 2006;49:406)
• 55 year old man with nodular swellings in abdominal wall and scrotum (Diagn Cytopathol 2001;24:36)

Pubic tumor with ill defined multinodular masses

• Composed primarily of large epithelioid cells with more atypia than classic epithelioid sarcoma
• Resembles rhabdoid tumor due to intracytoplasmic hyaline inclusions
• Large areas of necrosis and a multinodular pattern are common, but a granuloma-like pattern is uncommon

Perineal soft tissue mass

Chest wall

Back

Perineum

Keratin, CD34, neurofilament and p53

Case of the Week #69:

Large areas of necrosis

Infiltrative margins

Granuloma-like areas

Rhabdoid-like cells

EMA

CD34

PLAP negative

• Keratin, EMA, vimentin
• Variable desmin, CD34 and smooth muscle actin

• S100

• Epithelioid angiosarcoma
• Epithelioid MPNST: S100+, rarely EMA+, keratin negative
• Melanoma: S100+, usually HMB45+

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