HER2-positivity rates in breast cancer: no variation over time when clinicopathological features and testing are stable.

HER2 status is essential for breast cancer subtyping and for systemic treatment decisions as patients with HER2-positive tumours can benefit from anti-HER2 targeted therapies. However, few data are available on the current HER2-positive breast cancers rate and its evolution across years. Using data from the Côte d'Or breast cancer registry, we identified, between 1998 and 2011, 3220 women with invasive breast cancer diagnosed in the same laboratory which carries out regular internal quality controls and participates in multiannual international quality control programmes. Throughout the studied period of time, despite an increase of annual breast cancer cases, HER2 positivity rate remained stable (13.1%; P = 0.495), as did the proportion of tumours with positive hormone receptor status (P = 0.467) and the proportion of SBR grade II/III tumours (P = 0.747). Other characteristics, less strongly associated with HER2-positive status, showed either no annual variation (nodal and metastatic status, tumour size) or an annual positive trend (mean age, lobular carcinomas) or an annual negative trend (ductal carcinomas). These data reveal that in a population with stable clinical and pathological characteristics, and with the use of standardised assays, HER2 positivity rate remains stable over time. These results also emphasise that current HER2 positivity rate is lower than initially reported.