SOX10 expression in mammary invasive ductal carcinomas and benign breast tissue

SOX10 immunohistochemistry is used to identify tumors of neural crest origin, including melanocytic neoplasms. SOX10 expression has also been identified in myoepithelial cells of the breast and in a subset of invasive mammary carcinomas. In order to characterize SOX10 expression in ductal carcinomas of the breast, the aim of this study was to characterize the SOX10 in invasive ductal carcinomas according to molecular subtype, DCIS, and benign breast tissue. Forty cases of invasive ductal carcinoma of the breast were retrieved, with ten cases with immunohistochemical profile compatible with luminal A-like, luminal B-HER2-positive, non-luminal HER2-positive, and triple-negative subtypes. Whole tissue sections from each case were stained with SOX10. Six (60%) of ten triple-negative tumors were SOX10+ compared with 1 (3%) of 30 carcinomas of other molecular subtypes. All but one of the positive tumors showed at least moderate expression in at least 40% of tumor cells. All seven cases SOX10+ carcinomas were grade 3 tumors. Of the 13 cases with DCIS available for assessment, one (8%) showed positive SOX10 expression (a case associated with triple-negative carcinoma). Twenty-two cases contained normal breast tissue that showed SOX10 expression in both myoepithelial and luminal cells, predominantly patchy with variable intensity. SOX10 showed incomplete myoepithelial staining compared to other myoepithelial markers. In conclusion, SOX10 IHC cannot reliably differentiate between high-grade triple-negative carcinomas, melanomas, and myoepithelial tumors in the breast. SOX10 is not as robust a myoepithelial marker compared with other established markers.