Cytological Diagnosis of Metastatic Dedifferentiated Chondrosarcoma in Pleural Effusion: A Rare Case Report.

Dedifferentiated chondrosarcoma is a rare, high-grade malignant bone tumor distinguished by its highly aggressive clinical course. This primary bone malignancy is characterized by the coexistence of a low-grade cartilaginous component and an abrupt transition to a high-grade non-cartilaginous sarcoma. Although pulmonary metastases are common, pleural involvement presenting as malignant effusion is exceedingly rare and poorly documented in cytology literature. We report a case of a 49-year-old man with previously diagnosed pelvic dedifferentiated chondrosarcoma who presented with massive pleural effusion and multiple pulmonary nodules. Cytologic examination of the pleural fluid revealed scattered large pleomorphic malignant cells with moderate cytoplasm, irregular nuclear membranes, and prominent nucleoli, admixed with reactive mesothelial cells. Immunocytochemistry on cell block sections showed tumor cells positive for vimentin and negative for cytokeratin (AE1/AE3), calretinin, S-100, WT1, and IDH1 (R132H). Correlation with the prior histopathologic findings of the iliac bone lesion confirmed metastatic dedifferentiated chondrosarcoma involving the pleural cavity. To the best of our knowledge, this is the first reported case of cytology of DDCS in effusion cytology. This case highlights the exceptional metastatic potential of DDCS and underscores the critical role of cytology, supported by clinicoradiologic and immunocytochemical correlation, in diagnosing rare metastatic presentations in serous effusions.