Extraskeletal myxoid chondrosarcoma characterized by microtubular aggregates in the rough endoplasmic reticulum and tubulin immunoreactivity

A case is reported of a 66‐year‐old female with an extraskeletal myxoid chondrosarcoma which had originated in the lateral region of the right knee. The tumour tissue of the primary, recurrent, and metastatic deposits in the lungs was examined by electron microscopy and immunohistochemistry. Almost all the sarcoma cells in every tumour specimen harboured immunoreactivity to both a‐ and β‐subunits of S‐100 protein. A large population of cells in the subcutaneous tumour at autopsy had numerous parallel arrays of microtubules within the rough endoplasmic reticulum in addition to the well‐described ultrastructural features indicative of chondroblastic origin. These structures were present in round to polygonal, but not in fibroblastic, tumour cells. Tubulin immunoreactivity in the tumour cells showed the same tendency, being frequently positive in the large cells of the subcutaneous tumour but weakly positive in the fibroblastic and medium‐sized cells of the recurrent and metastatic tumours. The parallel arrays of intracisternal microtubules therefore may be composed of tubulin protein, as in ordinary cytoplasmic microtubules.