ASSESSMENT OF C-ERBB-2 AMPLIFICATION BY IMMUNOHISTOCHEMISTRY IN PARAFFIN-EMBEDDED BREAST-CANCER

The c-erbB-2 (HER-2/neu) proto-oncogenes is important in oncogenesis a nd for determination of prognosis in a number of human malignancies. D NA (Southern) hybridization and immunoblotting (Western) techniques ar e most commonly utilized for determining amplification status and prot ein expression of this proto-oncogene, respectively. These extraction techniques are often timeconsuming, costly, and subject to variability depending on the histological characteristics of the tumor. Paraffin- immunohistochemistry (P-IHC), on the other hand, is time and cost-effe ctive. In addition, this technique may offer enhanced sensitivity and specificity over extraction techniques due to the in situ nature of an alysis. In data presented here, 67 cases of human mammary carcinoma we re concomitantly assessed for c-erbB-2 gene copy number and oncoprotei n expression by dilutional DNA hybridization and P-IHC, respectively. In 64 (95.5%) of 67 cases, high level expression was associated with g ene amplification, whereas no detectable expression was associated wit h a normal diploid gene copy number. In two of the three discrepant ca ses, P-IHC predicted amplification not corroborated by Southern analys is. In these cases, tumor mass was limited by the intraductal componen t of the lesion or by an abundance of stromal elements within the spec imen. We conclude that P-IHC offers a favorable alternative to Souther n analysis in the assessment of c-erbB-2 gene copy number of this onco protein in human mammary carcinoma. Furthermore, immunohistochemistry may prove superior to either extraction technique in specimens with li mited tumor mass, such as biopsy materials, stroma-rich tumors, or ear ly stage lesions such as intraductal carcinoma.