Abstract P4-21-35: Phase II trial of pertuzumab, trastuzumab, and nab-paclitaxel in patients (pts) with HER2 overexpressing (HER2+) locally advanced or inflammatory breast cancer (LABC) or untreated stage IV metastatic breast cancer (MBC)

Background: Pathologic complete response (pCR) to HER2-targeting neoadjuvant therapy (NT) predicts for improved survival (Cortazar et al, Lancet, 2014). The addition of pertuzumab to trastuzumab and docetaxel increased pCR rates, and, as first line treatment for MBC led to longer overall survival ([OS] Swain et al, NEJM 2015). Avoidance of anthracyclines in the adjuvant setting for HER2+ BC reduced the risk of secondary hematologic malignancies without a detriment to OS (Slamon et al, NEJM, 20111). Finally, nab-paclitaxel (nab) might provide an advantage over other taxanes via decreased use of steroids and may lead to increased response rates (RR). We designed a study of pertuzumab (pert), trastuzumab (trast), and nab, testing the feasibility and efficacy of this regimen in the LABC and metastatic breast cancer settings. Materials and Methods: Pts with Stages II-III LABC received six cycles of NT with pert (day 1 q 21 days), trast, and nab 100 mg/m2 (both given IV, weekly). Pts with untreated MBC received the same regimen until progression, toxicities, or patient or physician preference led to stopping therapy. Primary endpoints included pCR (LABC) and RR and progression-free survival (PFS) in MBC. Forty pts with LABC and 25 pts with MBC were to be accrued. The study was designed to test whether the pCR rate of Neosphere (Gianni et al, Lancet Oncol, 2012, > 45.8%) and the PFS rate of CLEOPATRA (median of > 18.5 months) can be matched or exceeded. Procurement of serial samples for assessment of tumor gene expression, circulating tumor cells, miRNA, and serum DNA profiling for exploratory biomarker analysis was carried out. Results:Twenty-two of 28 already enrolled pts with LABC (clinical stage II:15, stage III: 7) completed NT. The median age was 53 (34-77). The pCR rate was 86% (6/7) for hormone receptor negative (HR-) and 40% (6/15) for HR+ pts, with an overall pCR of 55%. Three pts without pCR following NT had residual BC with a HER2 negative phenotype. Eighteen of 22 pts required nab dose modifications. The most frequent toxicities following NT included elevated liver function tests:27%, peripheral neuropathy:23%, hematological toxicities:17%, diarrhea:18%, infusion reactions:18%. In the MBC cohort there were 13 of 16 enrolled pts with > 2 months of follow-up. The median age was 47 (31-65), 62% had HR+ disease. A CR rate of 4/13 (31%) and confirmed RR of 77% were observed. The median number of cycles with pert, trast, nab was 9 (3+ to 41); 11 of 13 pts required dose modifications or delays (3 of the delays were due to primary breast surgery performed upon response to treatment). At a median follow-up of 19 months, PFS and OS estimates are 63% (95% CI 0.09-0.93), and 89% (95% CI 0.61-1.0). Conclusion: The non-anthracycline-containing regimen of pertuzumab, trastuzumab, and nab-paclitaxel induced a high pCR rate in HER2+ BC. PFS is encouraging in MBC. Outcome of the fully accrued cohorts inclusive of residual cancer burden scores in the LABC cohort, and correlative data with exploratory biomarker analysis will be presented. Citation Format: Somlo G, Frankel P, Yeon C, Yuan Y, Yim J, Kruper L, Taylor L, Mortimer J, Waisman J, Jones V, Vito C, Paz B, Huria A, Li D, Gaal C, Tong T, Tumyan L. Phase II trial of pertuzumab, trastuzumab, and nab-paclitaxel in patients (pts) with HER2 overexpressing (HER2+) locally advanced or inflammatory breast cancer (LABC) or untreated stage IV metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-21-35.