Abstract P2-16-31: The differential impact of non-anthracycline treatment regimens on pathological complete response (pCR) rates by ER status after neoadjuvant single or dual HER2 targeted therapy (NACT): A single centre experience

Abstract

Abstract Introduction: Dual HER2 targeting improved pCR rates (ypT0ypN0) compared with Herceptin plus chemotherapy in the TRYPHAENA and NeoSphere registration trials. Pertuzumab-containing regimens (FEC-THP and TCHP) were adopted at the Kent Oncology Centre (KOC) following national funding approval in December 2016. Methods: A retrospective study of 176 (stage 1-3) HER2+ breast cancer patients receiving HER2-directed NACT at KOC between November 2014- December 2018 was conducted. Single targeting treatment (S) used FEC-TH. Dual targeting (D) regimens were FEC-THP or TCHP. Data was collected on age, stage, grade, HER2 and ER status, treatment regimen, treatment completion, pCR (ypT0ypN0) status, and echocardiogram results. Results: 51 patients received single HER2 targeted FEC-TH prior to funding approval for Pertuzumab. 125 patients received dual HER2 targeted agents (60 FEC-THP, 65 TCHP). A slight excess of ER negative and node positive cancers was seen in the S group. Dual targeting increased pCR rates: 50.4% (D) vs 37.2% (S). Overall, pCR rates did not differ between the two D regimens (50% vs 50.7% for FEC-THP and TCHP respectively). Amongst D treated patients, pCR rates were greater in ER negative tumours with the highest pCR rates seen in those receiving TCHP. For ER positive patients both D regimens modestly increased pCR with no clear benefit to TCHP (table 1). FEC-THFEC-THPTCHPn516065pCR ERpos (%)414745pCR ERneg (%)335471 Early chemotherapy discontinuation rates were similar in both groups but interruptions in trastuzumab (H) treatment were more common in D, particularly the TCHP group (table 2). FEC-THFECTHPTCHPChemo stopped early19% (6)20% (12)20% (13)H stopped early0% (0)3% 2)0% (0)H± Pinterrupted2% (1)6.6% (4)12.3% (8) Conclusion: A substantial increase in pCR rates was observed with dual targeting, regardless of ER and nodal status, reproducing the registration trial data in real world clinical practice. pCR rates were greatest in D treated patients with ER negative cancers, regardless of treatment regimen. TCHP was the most effective D regimen in ER negative patients but did not deliver superior pCR rates to FEC-THP in ER positive breast cancers. Substantially more cardiac toxicity and H treatment interruptions were observed with D, particularly with TCHP therapy. Citation Format: Jessica Little, Samantha Forner, Van Sim, Russell Burcombe, Rema Jyothirmayi, Jennifer Louise Glendenning. The differential impact of non-anthracycline treatment regimens on pathological complete response (pCR) rates by ER status after neoadjuvant single or dual HER2 targeted therapy (NACT): A single centre experience [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P2-16-31.