Remarkably high frequency of EGFR expression in breast carcinomas with squamous differentiation.

The human epidermal growth factor receptor (EGFR) is reportedly overexpressed in 15-20% of breast carcinomas. EGFR overexpression is associated with reduced survival and is inversely correlated with expression of estrogen receptor (ER). This study assessed EGFR expression in breast carcinomas with squamous differentiation. The immunohistochemical (IHC) expression of EGFR was evaluated in 39 breast carcinomas with squamous differentiation (30 pure squamous, 6 adenosquamous, 3 carcinosarcomas) by use of the pharmDx assay (clone 2-18C9, DakoCytomation®). Cases were considered positive if at least 10% of the cells showed 1+ positivity in the squamous component. Squamous differentiation was confirmed with IHC for CK5-6 (clone D5/16B4, DakoCytomation®). ER, PR, and HER2 status as well as clinical information regarding treatment and outcome were correlated. As a control, a tissue microarray comprising 280 lymph node positive breast carcinomas was evaluated with the same EGFR assay. The 39 patients ranged in age ...