Abstract P4-15-01: Distinct early proliferation response to neoadjuvant anti-HER2 antibody drug conjugate +/- endocrine therapy in early breast cancer in the WSG ADAPT HER2+/HR+ trial
Authors: Gluz Oleg , Nitz Ulrike , Sherko Kuemmel , Stefan Kraemer , Braun Michael , Schumacher Claudia , Aktas Bahriye , Forstbauer Helmut , Reimer Toralf , Fasching Peter , Potenberg Jochem , Hofmann Daniel , Kates Ronald E , Wuerstlein Rachel , Christgen Matthias , Kreipe Hans H , Harbeck Nadia 
Published: May 2015

Background: HER2+, hormone receptor-positive (HR+) breast cancer is a distinct subtype associated with good prognosis but poor response to standard chemotherapy + anti-HER2 (single or dual blockade). Substantial overtreatment by poly-chemotherapy combined with anti-HER2 therapy is suspected in this subtype. Yet, the efficacy of combining endocrine therapy (ET) with anti-HER2 therapy or novel antibody drug conjugates like T DM1 without systemic chemotherapy remains unclear.

Methods: ADAPT HER2+/HR+ is a phase II, randomized, neoadjuvant, 3-arm trial (12 weeks) in patients with cT1c-cT3, cN0/+ HER2+, ER+ and/or PR+ early BC. Arm A: T-DM1 (3.6 mg/kg) alone; Arm B: T DM1 + ET (premenopausal: tamoxifen, postmenopausal: AI); Arm C: trastuzumab + ET. Postoperative chemotherapy is recommended together with completion of one year of trastuzumab. Initial and serial core biopsies were obtained prior to therapy and after 3 weeks. First translational analysis of the trial run-in phase (n=130) focuses on dynamics of HER2, Ki67, ER and PR.

Results: 162 tumors, HR+ and HER2+ by local pathology, were screened; n=130 were HR+ and HER2+ by central pathology and randomized at 40 trial sites in Germany between 11/2012 and 03/2014 (Arm A/B/C: 37/49/44).

Median age was 49 years; 60% were cT2-3, 32% cN+, 75% central G3; median baseline Ki67 was 30%; 49 patients were treated by TAM and 44 postmenopausal patients by AI in ET containing arms.

Three-week core biopsies were available in 117 patients (arm A/B/C: n=33/43/41), n=99 with invasive tumor tissue (61/76 (80%) in T-DM1 containing arms and 38/41(93%) in trastuzumab + ET arm). Three-week Ki67 could only be analyzed in n=73 (53% of patients in T-DM1-containing arms, 81% in the T+ET arm) due to a lacking amount of cells for counting (&lt;500).

Median fractional decrease in proliferation (Ki67) after 3 weeks of therapy was 40% in the T-DM1 + ET arm (B) as compared to 14% and 25% in the T-DM1 (A) and T+ET (C) arms, respectively. Among postmenopausal patients, the contrast (52% (B) vs. 0% (A) and 28% (B)) was significant. Mean PR expression change (absolute, measured in %) was -15 in the B Arm vs. 7 and -7 in the A and C arms, respectively (p=0.04) – particularly in postmenopausal women ( 25 vs. +13 and -10, respectively, p=0.04). Baseline ER expression was positively associated with early proliferation response (fractional Ki67 decrease), e.g., by logistic regression using 30% decrease as response criterion. Data on the impact of gene mutations and further molecular markers on proliferation response will be available for presentation at the meeting.

Conclusions: In the unique neoadjuvant ADAPT HER2+/HR+ trial, the combination of T-DM1 with ET (particularly AI) seems to be associated with a strong early proliferation response and PR expression drop in anti-HER2 antibody (drug conjugate) +/- ET, without systemic pre-operative chemotherapy. Interim analysis is scheduled after 130 completely treated patients. The high percentage of non-invasive tissue biopsied after 3 weeks in the T-DM1 arms is intriguing, as it would be consistent with higher pathological complete response rates.

Citation Format: Oleg Gluz, Ulrike Nitz, Kuemmel Sherko, Kraemer Stefan, Michael Braun, Claudia Schumacher, Bahriye Aktas, Helmut Forstbauer, Toralf Reimer, Peter Fasching, Jochem Potenberg, Daniel Hofmann, Ronald E Kates, Rachel Wuerstlein, Matthias Christgen, Hans H Kreipe, Nadia Harbeck. Distinct early proliferation response to neoadjuvant anti-HER2 antibody drug conjugate +/- endocrine therapy in early breast cancer in the WSG ADAPT HER2+/HR+ trial [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-15-01.