Intramuscular mixed tumour with clonal chromosomal changes

A case of an entirely intramuscular mixed tumour occurred in an 82-year-old man, who presented with a large mass in the region of the right triceps muscle. A lobulated tumour was seen, with plump, round epithelioid cells embedded in a chondromyxoid stroma. Immunohistochemical examination showed strong S100 protein and pancytokeratin positivity in most of the tumour cells. Cytogenetic analysis revealed complex clonal chromosomal changes: 47, XY, +i(2) (q10), -15, der(17) t(15; 17) (q11; p12), +r. Differential diagnosis against extraskeletal myxoid chondrosarcoma (EMC) may be problematic, particularly in an incisional biopsy. Chromosomal analysis can be very helpful in solving this problem, since EMC shows a specific reciprocal chromosome translocation characterised as t (9;22) (q22-31) (q11-12).