Soft tissue tumors: Extraskeletal myxoid chondrosarcoma

Macroscopic findings: the tumour presents as lobulated or multinodular mass, generally well circumscribed by a distinct fibrous capsule.The size of the tumour at the time of diagnosis may vary from 1 to about 20 cm (mean size: about 7 cm). Histology: typically, tumour nodules are composed of round or slightly elongated cells, with minimal features of chondroblasts, separated by mucoid substance; differentiated cartilage cells are rare; histological diagnosis may be very difficult, especially in highly cellular forms devoid of myxoid matrix. Tumour cells generally show positivity for vimentin, S100 protein, occasionally for EMA, and negativity for cytokeratin. A subset of tumours display neural or neuroendocrine differentiation as shown by positive immunohistochemical reactivities to neural or neuroendocrine markers such as neuron-specific enolase, synaptophysin, chromogranin A, and PGP9.5; tumours are mostly negative for markers (collagen type II, X, proteoglycan aggrecan) for the chondrocytic cell lineage. Ultrastructurally, at least one third of the tumours demonstrate microtubular aggregates within dilated rough endoplasmic reticulum; neurosecretory granules (80-170 nm diameter) are occasionally identified.