Abstract P2-09-12: Independent validation of the HER2-enriched subtype as a predictor of pathological complete response following trastuzumab and lapatinib without chemotherapy in early-stage HER2-positive breast cancer

Abstract

Abstract Background: HER2-positive breast cancer consists of 4 intrinsic molecular subtypes (Luminal A, Luminal B, HER2-enriched [HER2-E], and Basal-like) and a Normal-like subtype, with the HER2-E subtype having the highest activation of the EGFR-HER2 pathway. Concordant with this, the HER2-E subtype was significantly associated with pathological complete response (pCR) following lapatinib and trastuzumab without chemotherapy on the PAMELA phase II neoadjuvant trial (Lancet Oncol 2017). Here, we aimed to further validate this observation in a different cohort using tumor samples from the TBCRC023 trial. Methods: TBCRC023 (NCT00999804) was a randomized phase II trial combining a Simon Phase 2 design in the experimental arm with a pick-the-winner design, not powered for direct comparison. Ninety-seven women with HER2+ breast cancer measuring 2 cm or larger (median = 5 cm) were randomized in a 1:2 ratio to 12 vs. 24 weeks of lapatinib and trastuzumab. Letrozole (along with ovarian suppression if premenopausal) was added in patients whose tumors were also estrogen receptor (ER)-positive. All evaluable patients were assessed for pCR, defined as no residual invasive carcinoma in the breast. Intrinsic molecular subtypes from tumor biopsy formalin-fixed, paraffin-embedded samples taken at baseline (day 0) were determined with the nCounter-based PAM50 predictor. Gene expression PAM50 data was performed at Hospital Clínic in Barcelona blinded from clinical data. The primary outcome was the association of the HER2-E subtype (vs. non-HER2-E) with pCR. A logistic regression model adjusted for tumor size, ER status, nodal status and treatment arm was performed. Results: A total of 85 of the 97 (87.6%) baseline tumor samples were available. Most patients had the HER2-E subtype (51 [60.0%]), followed by Normal-like (12 [14.1%]), Basal-like (11 [13.0%]), Luminal B (7 [8.2%]) and Luminal A (4 [4.7%]). The proportion of patients with HER2-E tumors within ER+ and ER-negative disease was 54.9% and 67.7%, respectively. At the time of surgery, 17 of 85 patients (20.0%; 95% confidence interval [CI] 0.13-0.30) had a pCR in the breast. Fourteen of 51 patients with the HER2-E subtype (27.5%; 95% CI 0.17 to 0.41) and 3 of 34 patients with non-HER2-E subtypes (8.8%; 95% CI 0.03 to 0.23) achieved a pCR at the time of surgery (adjusted odds ratio 4.33; 95% CI 1.08-17.41; P=0.039). No other clinical-pathological variable was found significantly associated with pCR in the multivariable model. Conclusions: In an independent validation study performed while blinded to clinical outcomes, HER2-E subtype confirms its ability to identify patients with HER2-positive breast cancer who are likely to benefit from dual HER2 blockade therapies without chemotherapy. Further studies should be performed to prospectively validate this biomarker, alone or in combination with other biomarkers. Citation Format: Prat A, De Angelis C, Pascual T, Gutierrez C, Wang T, Paré L, Rexer B, Cortes J, Forero A, Llombart A, Wolff AC, Krop I, Galván P, Pavlick AC, Villagrasa P, Hilsenbeck SG, Schiff R, Osborne CK, Rimawi MF. Independent validation of the HER2-enriched subtype as a predictor of pathological complete response following trastuzumab and lapatinib without chemotherapy in early-stage HER2-positive breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-09-12.