Optimal adjuvant treatment for patients with HER2-positive breast cancer in 2015

The introduction of trastuzumab as adjuvant treatment for patients with HER2-positive breast cancer changed the natural course of early-stage disease. Currently, one year of trastuzumab given concurrently with a taxane and following an anthracycline regimen is the preferred standard of care in Europe. The first attempt to escalate this approach, though the implementation of dual HER2 blockade with lapatinib added to trastuzumab, as assessed by the ALTTO trial, failed to improve further clinical outcomes; clinical assessment of the adjuvant trastuzumab/pertuzumab regimen is still ongoing in the APHINITY trial. Negative results were also reported for the addition of bevacizumab to adjuvant trastuzumab treatment within the context of the BETH study. Similarly, efforts to de-escalate through shortening the duration of adjuvant trastuzumab treatment failed (the PHARE trial), whereas others are still ongoing. Of note, evidence supports the use of lighter chemotherapy regimens with one year of adjuvant trastuzumab as backbone, for women with small HER2-positive breast tumors, where the omission of anthracyclines did not compromise the clinical outcome. Despite the successes achieved so far, a proportion of women with early-stage HER2-positive breast cancer, will still experience disease recurrence. The identification of these women is urgently needed, as well as the identification of predictive biomarkers to dictate the optimal treatment strategy. So far, HER2 expression status has been the only validated predictive biomarker for this patient population. Despite the clear association of pCR achieved through neoadjuvant trastuzumab-based chemotherapy with clinical outcome, results from neoadjuvant trials have not been always consistent with what was seen in the adjuvant setting. Similarly, inconsistent results have been reported for the predictive ability of alterations affecting the PI3K signaling pathway or the quantification of tumor infiltrating lymphocytes. In the era of personalized oncology, rigorous translational and clinical collaborative efforts are needed to further advance the field of treatment of patients with HER2-positive breast cancer.