(P 153) DOES THE QUANTITY OF DEDIFFERENTIATION MATTER IN THE CLINICAL OUTCOMES OF DEDIFFERENTIATED CHONDROSARCOMA? A 10-YEAR SINGLE TERTIARY INSTITUTIONAL EXPERIENCE OF A SERIES.

Objective: Dedifferentiated chondrosarcoma (DD-CHS) is an aggressive primary bone sarcoma characterized by low-intermediate grade cartilage component with abrupt transition to a high-grade non-cartilaginous component. Though the dedifferentiated (DD) component is usually large, rarely it may be minimal ( < 5%) and may be missed altogether on initial presentation. There is no precedent data addressing the relevance of the amount of dedifferentiation in the overall prognosis of DD-CS. Prompted by a recent case of metastatic DD-CHS to the heart (previously diagnosed as primary cardiac undifferentiated pleomorphic sarcoma) who had only a minute focus of dedifferentiated (missed on prior evaluation), we performed a retrospective analysis of CC-CS in our institution over a 10-year period to determine the prevalence and the prognostic significance of the quantity of dedifferentiation in DD-CHS.

Methods: We performed a retrospective analysis of DD-CHS diagnosed between 2013 and 2023. The radiographic, clinicopathological, immunohistochemical, molecular features and follow up data were collected.

Results: A total of 21 patients were identified (15 males and 6 females). The mean age was 68.7 years with a male: female ratio of 2:1 (Table 1). The average tumor size was 11.1 cm (range 4.5 to 28.0 cm). 3 patients had minimal DD < 5% which were missed on initial evaluation, reported as intermediate grade conventional chondrosarcomas; and 18 had large DD (>5%). One case presented an undifferentiated pleomorphic sarcoma in the heart, suggesting a second primary but IDH1 mutation was positive and re-review showed < 5% DD. The second case presented with metastatic osteosarcoma, suggesting a second primary but re-review of the original pathology showed < 5% DD containing osteosarcoma. The third case presented as metastatic high grade spindle cell sarcoma in the acetabulum and re-review found < 5% DD in the sacrum. 7 locally recurred, 13 developed distant metastases, and 16 died of disease. (76%). Overall survival was slightly better in those with minimal DD than large DD, though not statistically significant (p=0.5). All three cases with minimal DD ( < 5%) died from disease.

Conclusion: DD-CHS is a highly aggressive neoplasm with a high mortality rate. The presence of dedifferentiation regardless of amount is predictive of aggressive biology and adverse outcome. This underscores an imperative need for thorough gross and histopathologic examination.

Table showing cohort information