Mesothelial markers in high-grade breast carcinoma.

AIMS: Advances in molecular profiling have subdivided breast carcinomas into distinct subtypes. Basal carcinomas are generally oestrogen receptor (ER)-progesterone receptor (PR)-/human epidermal growth factor receptor 2 (HER2)-, and cytokeratin (CK)5/6+. This profile overlaps with that of mesothelial cells. This study of high-grade breast carcinomas was undertaken to determine the expression of mesothelial markers. METHODS AND RESULTS: Immunohistochemistry was performed on 23 basal-like breast carcinomas and 30 high-grade breast carcinomas with variable ER, PR and HER2 expression. The incidence of staining of CK5/6, CK14, calretinin, Wilms' tumour 1 (WT1), thrombomodulin and epithelial membrane antigen was assessed statistically. CK14 staining was more specifically associated with triple-negative tumours than CK5/6. Calretinin positivity was statistically associated with basal-like carcinomas. WT1 and thrombomodulin expression was infrequent and limited to a small number of non-basal carcinomas. CONCLUSIONS: There is an overlap between the immunophenotype of mesothelial cells and that of basal-like carcinomas of breast. Positive calretinin and CK5/6 are not specific, and may be seen in both mesothelial cells and basal-like breast carcinomas. Negative ER and PR of basal carcinomas may also bias the observer against a breast origin. However, other negative mesothelial markers, such as WT1 and thrombomodulin, may help point to the correct diagnosis.