Extraskeletal myxoid chondrosarcoma: multimodal diagnosis and identification of a new cytogenetic subgroup characterized by t(9;17) (q22;q11)

Extraskeletal myxoid chondrosarcoma is a rare malignant soft tissue tumour that can be difficult to diagnose correctly, especially preoperatively. We describe four cases of extraskeletal myxoid chondrosarcoma of the extremiti es diagnosed by a multimodal approach. The cytological examination of fine- needle aspirates showed small and round, mildly pleomorphic cells lying in sheets and cords, but also dispersed within a myxoid and metachromatic inte rcellular substance. Histological, electron microscopic and immunocytochemi cal examination also yielded findings compatible with the diagnosis of extr askeletal myxoid chondrosarcoma. Cytogenetic analysis demonstrated a t(9;22 )(q22;q12) in two tumours and a t(9;17)(q22;q11) in the third and fourth. T he translocation t(9;22)(q22;q12) has been described repeatedly in extraske letal myxoid chondrosarcoma but never in other tumours; hence, the detectio n of this pathognomonic chromosome abnormality in shortterm cultured cells from fine-needle aspirates verified the diagnosis in two of the cases. The t(9;17)(q22;q11) found in the last two cases probably represents a new cyto genetic subgroup of extraskeletal myxoid chondrosarcoma as it, too, is unkn own in other contexts. The multimodal approach taken in these four cases en abled a definite diagnosis of a rare malignant tumour whose cytological and histological features alone are usually not sufficiently distinct to rule out other differential diagnostic possibilities.