Malignant Giant Cell Tumor of Bone: A Clinicopathological Analysis of 15 Cases.
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Malignant giant cell tumor of bone (MGCTB) refers to the presence of high-grade sarcomatous components within a giant cell tumor of bone (GCTB). MGCTB is classified into primary (PMGCTB) and secondary (SMGCTB) forms. It is extremely rare and often misdiagnosed as other sarcomas, especially when typical GCTB morphology is absent, leading to diagnostic pitfalls. In this study, we analyze 15 cases of MGCTB, reviewing clinical data, pathological features, immunohistochemistry, molecular characteristics, and follow-up outcomes. PMGCTB was found to be rarer than SMGCTB. Clinical symptoms predominantly include pain, mass detection, and restricted movement. MGCTB may lack GCTB components entirely, with malignant areas often presenting as high-grade sarcomas, though low-grade sarcomatous features can also be observed. Immunohistochemical markers such as H3.3G34W and H3G34W gene mutations exhibit high specificity and sensitivity for GCTB and MGCTB diagnosis. However, in cases with high dedifferentiation, few or absent mononuclear stromal cells may result in negative H3.3G34W expression and undetectable H3.3G34W gene mutations. The presence of high-grade sarcomatous morphology in a giant cell-rich tumor warrants thorough exclusion of PMGCTB. Additionally, misdiagnosis as SMGCTB can occur after denosumab treatment for GCTB. In conclusion, a comprehensive diagnostic approach combining patient age, tumor location, imaging, histology, immunohistochemistry, and molecular findings, with genetic testing when necessary, is essential for accurate diagnosis of GCTB and MGCTB. With a median follow-up of 12 months (range, 1-120 months), the 1-, 3-, and 5-year overall survival rates of the cohort were 76.9%, 76.9%, and 61.5%, respectively, and the median overall survival was not reached.