HER2 status in hormone receptor positive premenopausal primary breast cancer adds prognostic, but not tamoxifen treatment predictive, information.

Background Overexpression of human epidermal growth factor receptor 2 (HER2) or amplification of its gene is a prognostic factor in primary breast cancer and a predictor for tamoxifen treatment efficacy in oestrogen receptor (ER) positive disease. In the present study we explored a defined cohort of breast cancer patients included in a randomised trial in order to assess prognostic and tamoxifen treatment information yielded by HER2 status. Methods Premenopausal breast cancer patients with stage II tumours (n = 564) were included and allocated to 2 years of adjuvant tamoxifen treatment versus no adjuvant treatment. ER, progesterone receptor (PR) status and HER2 status was determined by immunohistochemistry using a tissue microarray. HER2 amplification was analysed by fluorescent in situ hybridisation and tumours being amplified and/or HER2 3+ were considered HER2+. HER2 status was evaluable in 83% of the patients and 12.6% were HER2+. In untreated patients, HER2 was a negative prognostic factor in ER+ patients, HR 2.95; 95% CI: 1.61–5.38, p < 0.001, but not in ER- patients, HR 0.67; 95% CI: 0.28–1.61, p = 0.4, and a significant interaction between the two markers was found, p < 0.01. HER2 status was not related to tamoxifen treatment efficacy in ER+ patients (term of interaction p = 0.95). When stratifying for PR status, similar results were achieved. Discussion HER2+ and ER+ breast cancer constituted a subgroup of tumours with poor prognosis in premenopausal breast cancer, whereas no treatment interaction was found between HER2 status and tamoxifen in ER+ tumours. The poor prognosis in HER2+ and ER+ patients may interfere with the interpretation of HER2 data in non-randomised trials of adjuvant tamoxifen