Estrogen Receptor-positive Ductal Carcinoma In Situ Frequently Overexpresses HER2 Protein Without Gene Amplification

Overexpression of human epidermal growth factor receptor 2 (HER2) protein is well known to be more frequent in ductal carcinoma in situ (DCIS) than in invasive ductal carcinoma (IDC). However, the reasons for this difference are poorly understood. On the basis of the high frequency of estrogen receptor-positive (ER+) and HER2-positive (HER2+) DCIS, we hypothesized that this tumor type overexpresses HER2 protein without gene amplification and retrospectively investigated the HER2/neu gene status of 71 ER(+)HER2(+) DCIS, surgically removed during the 2007 to 2017 period, employing fluorescence in situ hybridization (FISH). To compare HER2 protein expressions between in situ and invasive components of individual tumors, 86 pT1mi/1a IDC with predominantly in situ disease were also examined. Furthermore, for comparison of FISH status between in situ and coexisting invasive components, another patient cohort, 78 FISH-positive IDC cases, were employed. To elucidate biological differences among DCIS with various combinations of ER and HER2 protein expressions, we also analyzed public microarray data of mRNA. HER2 gene amplification was observed in 35% of ER(+) and HER2 protein-overexpressing specimens, significantly lower than the 94% in ER-negative (ER−) and HER2 protein-overexpressing specimens (P
Source: The American Journal of Surgical Pathology - Category: Pathology Tags: Original Articles Source Type: research