45 ErbB2 overexpression affects tamoxifen efficacy in the adjuvant treatment of node negative operable breast cancer patients

Abstract

Aim To study retrospectively the interaction between ErbB2 overexpression and adjuvant tamoxifen in node negative breast cancer patients (pts) entered into the controlled clinical trial GUN-I (Lancet 1988, ii: 1095) Patients and Methods ErbB2 was evaluated by immunohistochemistry in 150 out of 173 pts who had been randomly assigned to 2-year adjuvant tamoxifen (TM) (n. = 90) or no further therapy (n. = 60). ErbB2 was defined positive if more than 10% of cells showed specific membrane staining. Results As of November 30, 1994, median follow up is 12 years. ErbB2 was overexpressed in 44/l50pts (29.3%). The addition of ErbB2 to a multivariate Cox model, containing age, menopausal status, tumor size, nuclear grade and treatment as covariates, was not statistically significant, while the addition of first order interaction between ErbB2 and TM was statistically significant both for DFS and OAS; the same result was obtained also when the basal model contained estrogen receptor (ER) and ER-TM interaction. Indeed, adjuvant tamoxifen significantly prolonged DFS ( P = 0.0009) and OAS ( P = 0.03) only among ErbB2 negative cases, while no difference was observed in ErbB2 positive cases both for DFS ( P = 0.22) and for OAS ( P = 0.12). Dr. De Laurentiis is recipient of an AIRC fellowship.