Abstract P5-18-20: Phase II study of pertuzumab, trastuzumab, and weekly paclitaxel in patients with metastatic HER2-overexpressing metastatic breast cancer.

Background: Pertuzumab (P) is a monoclonal antibody which binds to extracellular domain II of HER2 distally from trastuzumab (H), disrupting HER2 dimerization and signaling. The CLEOPATRA phase III trial showed that HP + docetaxel in HER2+ metastatic breast cancer (MBC) prolonged progression-free survival (PFS) compared to placebo + H + docetaxel. We report preliminary results of a phase II study to evaluate the safety and efficacy of weekly paclitaxel with HP (THP). Methods: Patients (pts) with HER2+ MBC with 0–1 prior treatment (Rx) are eligible. Pts receive weekly (w) paclitaxel (80mg/m 2 ), q3w trastuzumab (loading dose 8mg/kg → 6mg/kg), and q3w pertuzumab (flat loading dose 840mg → flat dose 420mg). The primary endpoint is PFS at 6 months (mo). Secondary endpoints include response, safety (including cardiac events), and tolerability. Evaluable pts are those who have started study Rx and are assessed at 6 mo for PFS. Left ventricular ejection fraction (LVEF) is monitored by echocardiogram every 3 mo. Cardiac events are defined as symptomatic LV systolic dysfunction (LVSD), non-LVSD cardiac death, or probable cardiac death. Results: As of 6–1-12, 38 of the planned 69 pts were enrolled and 20 pts were evaluable at 6 mo. Median age is 52 years (range 32 to 72). A total of 11 pts (55%) previously received trastuzumab in the adjuvant or metastatic setting, and 8 pts (40%) were being treated in the second-line metastatic setting. Of the 20 evaluable pts, G 3/4 toxicities were sepsis (1 pt, 5%), cholecystitis (1 pt, 5%), fatigue (1 pt, 5%), skin ulceration (1 pt, 5%) and cystic macular degeneration (1 pt with prior prolonged Rx with paclitaxel, 5%). Common G 1/2 toxicities included alopecia (20 pts, 100%), peripheral neuropathy (20 pts, 100%), fatigue (18 pts, 90%), ALT/AST elevation (17 pts, 85%), diarrhea (15 pts, 75%), rash (13 pts, 65%), nail changes (10 pts, 50%), mucositis (9 pts, 45%), dry skin (8 pts, 40%), and nausea (8 pts, 40%). Median LVEF was 64% at baseline (range 50% to 69%), 60% at 3mo (range 50% to 73%), and 60% at 6mo (range 49% to 67%). There were no cardiac events. At 6 mo, 15/20 pts (75%) were progression-free (2 CR, 8 PR and 5 SD); 5 pts had progressed. The 6 mo PFS results for all 38 enrolled patients will be updated. Conclusions: Our single-center phase II study continues to accrue, with no clinically significant diarrhea or signal of increased cardiac toxicity to date. Pertuzumab was recently FDA-approved in combination with trastuzumab and docetaxel. If the estimate of safety and activity is similar to results with docetaxel in CLEOPATRA, this study will provide support for weekly paclitaxel as an alternative option in combination with trastuzumab and pertuzumab in this setting. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-18-20.