c-erbB2 overexpression decreases the benefit of adjuvant tamoxifen in early-stage breast cancer without axillary lymph node metastases

Purpose: We studied retrospectively the interaction between c-erbB2 overexpression and adjuvant tamoxifen in node-negative breast cancer patients enrolled in the Gruppo Universitario Napoletano 1 (GUN-1) trial. Patients and Methods: c-erbB2, evaluated by immunohistochemistry in 145 of 173 patients randomly assigned to 2-year adjuvant tamoxifen or no further therapy, was considered overexpressed if greater than 10% of the cells showed specific membrane staining. The role of each prognostic variable and their independent effect were studied using the Cox model. Disease-free (DFS) and overall (OAS) survival curves were estimated by the Kaplan-Meier method. Results: As of November 30, 1994, the median follow-vp period was 12 years. c-erbB2 was overexpressed in 43 of 145 patients (29.7%), which directly correlated with tumor size and inversely with estrogen receptor (ER) level. At univariate analysis, overexpression of c-erbB2 did not affect either DFS or OAS; tamoxifen had a greater effect on reducing the risk of recurrence than of death. Addition of c-erbB2 to a multivariate Cox model that contained menopausal status, tumor size, nuclear grade, and treatment as covariates did not affect the significance of the model for DSF or OAS, whereas addition of the first-order interaction between c-erbB2 and tamoxifen was statistically significant both for DFS and OAS. The same result was obtained when the model contained ER status and ER-tamoxifen interaction. Indeed, adjuvant tamoxifen significantly prolonged DFS and OAS in c-erbB2-negative cases, whereas it had no effect on DFS and OAS in c-erbB2-positive patients. Conclusion: In early-stage breast cancer patients, overexpression of c-erbB2 is a marker of lock of efficacy of adjuvant tamoxifen. (C) 1996 by American Society of Clinical Oncology.