[Primary skull base chondrosarcoma: a clinicopathological analysis].

Objective: To investigate the clinicopathological features, immunophenotype, molecular characteristics and differential diagnosis of primary skull base chondrosarcoma. Methods: Nine cases of primary skull base chondrosarcoma were collected at the First Affiliated Hospital of Fujian Medical University, from January 2006 to June 2019, reviewed for the clinical and radiologic data and morphologic features, immunophenotype and molecular characteristics. Results: Among all the 9 cases, six were male, three were frmale, with average age 47 years, and median age 47 years; five cases were WHO gradeⅠ, and four were WHO grade Ⅱ. Microscopically, the tumor showed lobulated growth pattern with low-medium cellularity within a chondroid or mucoid background. The tumor cells showed mild-moderate atypia, with binucleated forms, and mitosis was rare or occasional. Immunohistochemistry (IHC) showed tumor cells were positive for S-100 protein, vimentin, SOX-9 and D2-40, and negative for Brachyury, CK, EMA and CK8/18; the Ki-67 index was low (1% to 5%). Molecular analysis showed IDH1 R132C mutation in four cases. Conclusions: Skull base chondrosarcoma is a rare cartilaginous malignant tumor with a good prognosis. Its characteristic morphologies, combined with IHC and molecular detection are helpful for the differential diagnosis.