Abstract P6-07-06: Effect of serum biomarkers (activin A, CAIX, HER2, TIMP-1, and uPA) on outcome in HER2+ metastatic breast cancer patients treated in first line with lapatinib or trastuzumab combined with taxane: CCTG MA.31

Background: In MA.31, the lapatinib-taxane combination led to shorter PFS than trastuzumab-taxane in HER2+ metastatic breast cancer. We investigated the prognostic and predictive effects of pretreatment serum biomarkers. Methods: MA.31 accrued 652 patients; 537 (82%) were centrally-confirmed HER2+. Biomarkers were categorized for univariate and multivariate predictive investigations with a median cut-point, ULN cut-points (15 ng/ml- HER2; 506 pg/ml- CAIX; 454 pg/ml- TIMP-1; 1940 pg/ml– uPA; 600 pg/ml- activin A), and custom cut-points (30 and 100 ng/ml for HER2). Stratified step-wise forward Cox multivariate analysis used continuous and categorical biomarkers for PFS in the ITT and central HER2+ populations; central HER2+ biomarker results are shown. Results: Serum was banked for 472 (72%) of 652 patients. Higher serum activin A (>median; >ULN; p median; >ULN; p=0.02; p=0.001); higher HER2 (>median; >15; >30; or >100 ng/ml; p=0.05-0.002) and higher TIMP-1 (>median; >ULN; p=0.001; p=0.02) had shorter univariate PFS. In multivariate analysis for PFS: higher continuous activin A (HR=6.75 with Box-Cox transformation, P Conclusions: Higher serum activin A was a significant independent prognostic biomarker of shorter progression-free and overall survival. No serum biomarker was predictive of differential response to lapatinib vs. trastuzumab. Evaluation of activin A and CAIX-targeted therapy in addition to HER2-targeted therapy may be warranted in patients with elevated serum levels of these biomarkers. *AK, MH, DH, & JH contributed equally Grant: PA Breast Cancer Coalition. Citation Format: Kang A, Hupp M, Ho D, Huang J, Leitzel K, Ali S, Shepherd L, Parulekar WR, Ellis CE, Rocco CJ, Zhu L, Virk S, Nomikos D, Aparicio S, Gelmon KA, Truica C, Al-Marrawi Y, Rizvi S, Vasekar M, Nagabhairu V, Polimera H, Marks E, Richardson A, Ali AS, Krecko L, Carney WP, Downs S, Chen BE, Lipton A. Effect of serum biomarkers (activin A, CAIX, HER2, TIMP-1, and uPA) on outcome in HER2+ metastatic breast cancer patients treated in first line with lapatinib or trastuzumab combined with taxane: CCTG MA.31 [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 P6-07-06.