Adding a second HER2-blocker, pertuzumab (Perjeta) to standard care therapy trastuzumab (Herceptin) after surgery may be modestly beneficial for women with HER2-positive breast cancer, according to results of a phase 3 clinical trial presented at the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting.

In this study, 4805 patients with HER2-positive, early breast cancer were randomly assigned to receive standard adjuvant chemotherapy for 18 weeks plus 1 year of either trastuzumab and placebo or trastuzumab and pertuzumab.

At an early follow-up of 3 years, 93.2% of women who received trastuzumab alone had not developed invasive disease compared with 94.1% of those who received pertuzumab and trastuzumab, a difference of 1%. While the prognosis for patients who receive trastuzumab is already favorable, patients in the study who received pertuzumab and trastuzumab had a 19% lower chance of developing invasive breast cancer than those who received trastuzumab alone.

At a median follow up of almost 4 years, 171 (7.1%) patients in the pertuzumab arm had developed invasive breast cancer, compared with 210 (8.7%) patients in the placebo arm. The benefit from pertuzumab appeared slightly greater among patients with node-positive disease. The rates of serious side effects were low and similar in both groups.

These findings suggest that it may be possible to further improve outcomes for some women by adding a second HER2-targeted treatment, without increasing risk for serious adverse effects. Trastuzumab targets only HER2, whereas pertuzumab blocks HER2 and HER3. Using both antibodies establishes a more complete blockade of cancer cell growth signals and may lower the chance of treatment resistance, according to the researchers. 

Reference

1. Von Minckwitz G, Procter MJ, de Azambuja Ev, et al. APHINITY trial (BIG 4-11): a randomized comparison of chemotherapy (C) plus trastuzumab (T) plus placebo (Pla) versus chemotherapy plus trastuzumab (T) plus pertuzumab (P) as adjuvant therapy in patients (pts) with HER2-positive early breast cancer (EBC). J Clin Oncol. 2017;35(suppl):abstr LBA500.