Rimawi M, et al. - In patients with human epidermal growth factor receptor 2 (HER2)–positive and hormone receptor–positive metastatic/locally advanced breast cancer (MBC/LABC), researchers evaluated pertuzumab plus trastuzumab and an aromatase inhibitor (AI) in the PERTAIN trial. According to findings, this trial failed to meet its primary progression-free survival (PFS) end point. Pertuzumab plus trastuzumab and an AI was proved to be efficacious for the treatment of HER2-positive MBC/LABC, and demonstrated a safety profile that was consistent with previous trials of pertuzumab plus trastuzumab.

Methods

• In the PERTAIN trial, which is an ongoing randomized, open-label, multicenter—80 sites and eight countries—phase II trial, patients having HER2-positive, hormone receptor–positive MBC/LABC and no prior systemic therapy with the exception of endocrine were included.
• Participants were randomly assigned (1:1) to intravenous pertuzumab (840 mg loading dose followed by 420 mg every 3 weeks) plus trastuzumab (8 mg/kg followed by 6 mg/kg every 3 weeks), and oral anastrozole (1 mg every day) or letrozole (2.5 mg every day), or trastuzumab and an AI.
• At the investigator’s discretion (decided before but given after random assignment), induction intravenous docetaxel every 3 weeks or paclitaxel every week could be administered for 18 to 24 weeks.
• Progression-free survival (PFS) was assessed as primary end point.
• Stratification of patients was done based on whether they received induction chemotherapy and their time since adjuvant hormone therapy.

Results

• Per arm, random assignment involved 129 patients (February 2012 to October 2014; intent-to-treat populations); 75 in one arm and 71 in the other were chosen to receive induction chemotherapy.
• In the pertuzumab plus trastuzumab arm, stratified median PFS was 18.89 months (95% CI, 14.09 to 27.66 months).
• In the trastuzumab arm, stratified median PFS was 15.80 months (95% CI, 11.04 to 18.56 months) (stratified hazard ratio, 0.65; 95% CI, 0.48 to 0.89; P=.0070).
• Serious adverse events (AEs) were experienced by 42 (33.1%) of 127 and 24 (19.4%) of 124 patients in the safety populations of the pertuzumab plus trastuzumab and trastuzumab arms, respectively.
• Data showed that rates of grade ≥ 3 AEs were 64 (50.4%) of 127 and 48 (38.7%) of 124, respectively.
• No AEs-related deaths were reported.