Dedifferentiated chondrosarcoma with minimal or small dedifferentiated component.

Dedifferentiated chondrosarcoma (DDCS) is an aggressive bone sarcoma characterized by low-intermediate grade cartilage component with abrupt transition to a high-grade non-chondrosarcomatous component. Generally, the dedifferentiated (DD) component is large. However, rare cases have minimal (<1 cm) or small (1-2 cm) areas of DD. We describe the clinicopathologic features of such tumors and evaluate the prognostic significance of this finding compared to cases with large DD (>2 cm). Available slides were re-reviewed for assessment of histologic features. The medical record was reviewed for imaging studies and clinical characteristics. Thirty-five cases were included. Six patients had minimal DD, four had small DD and 25 had large DD. None of the minimal DD showed definitive imaging evidence of DD. Two minimal DD (33%) locally recurred and 2 (33%) developed distant metastases. None of the small DD cases showed definitive imaging evidence of DD. None of the small DD locally recurred and at least 1 (25%) developed distant metastases. There was no significant difference in age, gender, pelvic site, tumor size >8 cm, tumor necrosis or undifferentiated pleomorphic sarcoma-like morphology between minimal or small DD compared to large DD, though osteosarcomatous differentiation was significantly more common in large DD. There was no significant difference in overall survival between minimal or small DD compared to large DD (p = 0.81 and p = 0.17, respectively), or in progression-free survival (p = 0.47 and 0.29, respectively), or metastasis-free survival (p = 0.06 and 0.62, respectively). DDCS with minimal or small DD show similar demographic distribution, anatomic localization and histologic features to large DD. DD in these cases is unlikely to be detected on imaging. Furthermore, at least a subset of these tumors is extremely aggressive despite the limited extent of DD. This highlights the need for thorough gross and histologic examination and sampling.