Expression of calretinin by breast carcinoma and the potential for misdiagnosis of mesothelioma.

AIMS

Calretinin and cytokeratin (CK)5/6 are frequently used to differentiate between metastatic breast cancer and primary malignant mesothelioma in pleural biopsies, but both tumours may express these markers. This study was aimed at evaluating the frequency of calretinin expression in primary breast carcinomas, and assessing the characteristics of the calretinin-positive tumours.

METHODS AND RESULTS

Fifty-three primary breast adenocarcinomas were analysed for immunohistochemical expression of calretinin. CK5/6 and epidermal growth factor receptor (EGFR) immunostaining were performed on the calretinin-positive subset. Tumours were classified as basal-like if they met standard morphological and immunohistochemical criteria. Fifteen per cent (8/53) of the breast tumours were positive for calretinin. Eighty-eight per cent (7/8) of the calretinin-positive tumours were grade 3, as compared with 20% (9/45) of the calretinin-negative tumours (P<0.001). Only 13% (1/8) of the calretinin-positive tumours were also oestrogen receptor (ER)-positive, as compared with 87% (39/45) of the calretinin-negative tumours (P<0.001). Eleven per cent (6/53) of the tumours were classified as basal-like. Of these, four were positive for calretinin and two were negative (P=0.003).

CONCLUSIONS

Fifteen per cent of breast carcinomas stain with calretinin. These tumours are more likely to be high-grade, ER-negative, and display a basal-like phenotype. These tumours may be misdiagnosed as malignant mesothelioma when they metastasize to the pleura.