c-erbB2 oncoprotein expression, gene amplification, and chromosome 17 aneusomy in apocrine adenosis of the breast.

Amplification of the c-erbB2 oncogene and numerical aberrations of chromosome 17 occur in human breast carcinomas. Apocrine adenosis (AA) of the breast has been shown occasionally to have c-erbB2 overexpression and a possible premalignant potential, but little is known about cellular level genetic alterations in AA of the breast. Fluorescence in situ hybridization (FISH) is a new approach to detect these. In this study, a series of AA was studied by immunohistochemistry for c-erbB2 protein expression and by FISH using dual colour DNA probes for the c-erbB2 gene and the centromeric region of chromosome 17. Cell membrane immunostaining was seen in 10/18 (55.6%) AA cases, but unequivocal c-erbB2 gene amplification or chromosome 17 aneusomy was not seen. The results of this study suggest that c-erbB2 overexpression without amplification may occur early in breast oncogenesis. Amplification and numerical chromosome aberrations may occur later in the pathogenesis of apocrine-derived breast carcinomas.