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.