Sox10 is expressed in primary melanocytic neoplasms of various histologies but not in fibrohistiocytic proliferations and histiocytoses

BackgroundSox10 is a transcription factor associated with neural crest development. Its expression has been reported in melanocytes and peripheral nerve sheath cells and their associated tumors.ObjectiveTo assess Sox10 sensitivity in benign and malignant melanocytic neoplasms of various histologic subtypes and to discern the specificity of Sox10 in distinguishing between melanocytic neoplasms and fibrohistiocytic and histiocytic mimickers.MethodsSox10 expression was examined by immunohistochemistry in 145 cases of formalin-fixed paraffin-embedded tissue, including benign and malignant melanocytic lesions of various histologies and stages (n = 83), fibrohistiocytic and histiocytic lesions (n = 33), and peripheral nerve sheath tumors (n = 19), among others (n = 10).ResultsImmunoreactivity with Sox10 was observed in 100% (83/83) of benign and malignant melanocytic lesions of various subtypes, as well as in 100% (19/19) of benign and malignant peripheral nerve sheath lesions. Among the fibrohistiocytic proliferations and histiocytoses examined, Sox10 was negative in all cases (0/33). Sox10 expression did not vary by histologic subtype in nevi or melanoma; however, both the percentage of tumor nuclei demonstrating Sox10 expression and the intensity of expression were inversely correlated with malignant potential (nevi, melanoma in situ, invasive and metastatic melanoma) (P < .001, P = .016, respectively). Malignant peripheral nerve sheath tumors also showed decreased mean Sox10 expression and decreased intensity of expression when compared with benign counterparts (P < .001, P = .021, respectively).LimitationsThis is a retrospective study with 145 cases included.ConclusionsSox10 is a highly sensitive marker for melanocytic proliferations and may be useful diagnostically when the differential diagnosis includes fibrohistiocytic and histiocytic proliferations demonstrating S100 expression.