Phase II Study of Weekly Paclitaxel with Trastuzumab and Pertuzumab in Patients with Human Epidermal Growth Receptor 2 Overexpressing Metastatic Breast Cancer: 5-Year Follow-up

Background: Favorable progression-free survival (PFS) and overall survival (OS) results were previously reported on a phase II trial of patients with human epidermal growth receptor 2 (HER2)-positive metastatic breast cancer (MBC), treated with weekly paclitaxel in combination with trastuzumab and pertuzumab in the first- and second-line setting, with a median follow-up of 33 months. Here, we report updated PFS and OS results with more than 2 years of additional follow-up.

Materials and methods: In this phase II study, adult patients with HER2-positive MBC who received no or one prior therapy received intravenous paclitaxel (80 mg/m² weekly) with trastuzumab (8 mg/kg loading dose followed by 6 mg/kg every 3 weeks) and pertuzumab (840 mg loading dose followed by 420 mg every 3 weeks), administered in 21-day cycles. Primary endpoint was 6-month PFS, and secondary endpoints included median PFS and OS.

Results: From January 2011 to December 2013, 69 patients were enrolled: 51 (74%) and 18 (26%) were treated in first- and second-line metastatic settings, respectively. As of August 21, 2017, the median follow-up was 59 months (range, 20-75 months; 67 [97%] patients were evaluable for efficacy). The 6-month PFS was 86% (95% confidence interval [CI] 0.76-0.93). The median PFS was 24.2 months (95% CI 17-35) for the overall population; it was 25.7 months (95% CI 17.0 to not reached) and 20.1 months (95% CI 8.5-33.0) for patients with no and one prior treatment, respectively. The median OS was not reached for the overall group; it was not reached and 39.7 months (95% CI 32.9-66.7) for patients with no and one prior treatment, respectively. Treatment was well tolerated with no additional safety concerns.

Conclusion: With a longer follow-up of almost 5 years, combination of weekly paclitaxel, trastuzumab, and pertuzumab remains effective with a favorable median PFS and a median OS not reached.

Implications for practice: The combination of weekly paclitaxel, trastuzumab, and pertuzumab has been endorsed by the National Comprehensive Cancer Network as one of the first-line treatment options in patients with human epidermal growth receptor 2 (HER2)-positive metastatic breast cancer (MBC). However, the long-term safety and efficacy are still unknown. Findings from this phase II study provide favorable preliminary data on the safety and efficacy of trastuzumab and pertuzumab in combination with weekly paclitaxel at 5-year follow-up, and it remains an effective first-line treatment option for patients with HER2-positive MBC.