• Also known as melanoma of soft parts
• Rare aggressive tumor of adolescents / young adults
• Median age 30 years, range 13-73 years; 60% male
• Deep soft tissues of extremities, trunk or limb girdles, tends to occur near tendon, fascia or aponeuroses
• Slow progression, frequent local recurrences; eventually nodal and distant metastases
• 5 year overall survival is 63% (Am J Surg Pathol 2008;32:452)
• Size is most significant prognostic factor (Dermatol Res Pract 2012;2012:984096)

• 35 year old woman with tumor of foot (Case Rep Oncol 2012;5:449)
• 40 year old man with cutaneous tumor of lower leg (J Lab Physicians 2012;4:53)
• 53 year old Caucasian man with painful lesion on arm (Indian J Dermatol 2009;54:168)

• Complete surgical resection

Arm

• Firm, well circumscribed, gray-white, gritty sensation when cutting
• Median 4 cm, range 1-15 cm
• Variable necrosis

• Distinctly nested growth pattern with mixture of spindle, epithelioid and tumor giant cells
• Melanin pigment in 2/3
• May have floret-like multinucleated giant cells
• Often rhabdoid cells, bizarre pleomorphic cells
• Usually necrosis
• Mean 4 MF/10 HPF

Various images

Arm

Foot tumor

Lower leg tumor

Spindled and epithelioid cells

Microphthalmia transcription factor

• Variable cellularity, may form microacinar structures resembling adenocarcinoma (Am J Clin Pathol 2002;117:217)

• S100, HMB45, microphthalmic transcription factor (75%, Mod Pathol 2001;14:6), melanoma-cell adhesion molecule, MelanA (43%), iron (intra- and extracellular), Leu7/CD57, vimentin, keratin (variable)

• Alpha-smooth muscle actin, desmin, CAM 5.2

• Melanosomes

• t(12;22)(q13;q12): ATF1 and EWS (not seen in melanoma)
• Usually diploid or less aneuploidy than metastatic melanoma to soft tissue
• Tumors in GI tract may have a variant fusion gene EWSR1-CREB1

FISH

• Melanoma

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