Clinicopathological characteristics of the SOX10+ subset of HER2+ breast cancer.

HER2-positive breast cancers (HER2+ BC) are a heterogeneous group of tumors with variable clinical behavior. SOX10, a biomarker that has been studied in the context of breast carcinomas, especially triple-negative breast carcinomas (TNBC), has yet to be systematically investigated in a cohort of HER2+ BC. Our aim was to investigate the clinicopathological features of the SOX10+ subset of HER2+ BC. 80 HER2+/ER- invasive breast carcinomas were stained for SOX10. All SOX10+ cases and a matched number of SOX10- cases were also stained for vimentin and androgen receptor (AR). 18 % (14/80) of our cases were SOX10+. SOX10 expression was seen in both IHC positive (3+) and equivocal (2+) but ISH-amplified cases. The SOX10+ tumors were significantly associated with both greater vimentin expression (36 % vs 0 %, p = 0.0407) and less AR expression (14 % vs 100 %, p = 0.0001) compared to SOX10- tumors. Interestingly, the vimentin+/AR- subset of our SOX10+ cases showed uniformly apocrine-like morphology, while all SOX10- cases, including those with apocrine-like morphology, were vimentin-/AR+. Our findings suggest that SOX10+/HER2+ BC are more likely to show a peculiar apocrine-like, vimentin+/AR- phenotype as compared to SOX10-/HER2+ BC.