In the phase II PERTAIN trial reported in the Journal of Clinical Oncology, Rimawi et al found that adding pertuzumab to trastuzumab plus an aromatase inhibitor improved progression-free survival in patients with advanced HER2-positive, hormone receptor–positive breast cancer.
In the trial, 258 patients with locally advanced or metastatic disease and no prior systemic therapy except endocrine therapy from 80 sites in 8 countries were randomized between February 2012 and October 2014 to receive pertuzumab (840-mg loading dose). That was then followed by 420 mg every 3 weeks plus trastuzumab at 8 mg/kg, followed by 6 mg/kg every 3 weeks and oral anastrozole at 1 mg daily or letrozole at 2.5 mg daily (n = 129) or trastuzumab and an aromatase inhibitor (n = 129).
Induction docetaxel every 3 weeks or paclitaxel every week was given for 18 to 24 weeks at investigator discretion (decided before randomization) and was received by 75 patients in the pertuzumab group and 71 patients in the control group.
The primary endpoint was progression-free survival. Patients were stratified by receipt of induction chemotherapy and time since adjuvant hormone therapy.
Median progression-free survival was 18.89 months in the pertuzumab group vs 15.80 months in the control group (stratified hazard ratio [HR] = 0.65, P = .0070). Median progression-free survival was 21.72 months vs 12.45 months (HR = 0.55, 95% confidence interval [CI] = 0.34–0.88) among patients not receiving induction chemotherapy and 16.89 months vs 16.85 months (HR = 0.75, 95% CI = 0.50–1.13) among those receiving induction chemotherapy. Among 215 patients with measurable disease at baseline, response was observed in 63.3% vs 55.7% of patients (P = .2537). Median duration of response was 27.10 months vs 15.11 months (P = .0181). Overall survival data were not mature at the time of analysis, with median survival not being reached in either group.
Grade ≥ 3 adverse events occurred in 50.4% of the pertuzumab group, with the most common being hypertension (10.2%) and diarrhea (7.1%), vs 38.7% of the control group, with the most common being hypertension (11.3%) and neutropenia (6.5%). Grade ≥ 3 left ventricular dysfunction occurred in 3 patients in the pertuzumab group (2.3%) and no patients in the control group. Serious adverse events occurred in 33.1% vs 19.4% of patients. Adverse events led to discontinuation of pertuzumab in 10.2% of patients. No deaths due to adverse events were reported.
The investigators concluded, “PERTAIN met its primary [progression-free survival] endpoint. Pertuzumab plus trastuzumab and an [aromatase inhibitor] is effective for the treatment of HER2-positive [metastatic/locally advanced breast cancer]. The safety profile was consistent with previous trials of pertuzumab plus trastuzumab.”
Mothaffar Rimawi, MD, of the Dan L. Duncan Comprehensive Cancer Center, Baylor College of Medicine, is the corresponding author for the Journal of Clinical Oncology article.
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