Abstract Background: Everolimus (EVE) plus exemestane (EXE) doubled progression-free survival (PFS) while maintaining quality of life versus EXE alone in postmenopausal women with hormone receptor positive (HR+), HER2-negative metastatic breast cancer (mBC) (BOLERO-2 phase 3; NCT00863655). Pretreatment serum activin A was previously reported as a prognostic factor in first-line hormone therapy (letrozole vs tamoxifen) (Novartis P025) and anti-HER2 mBC (lapatinib vs trastzmab) (CCTG MA.31) trials. Here we investigate the prognostic and predictive ability of activin A in BOLERO-2. Methods: Activin A levels were determined on pretreatment serum samples using ELISA. Cox-proportional hazards model was used to assess the efficacy of EVE in the activin A low and high subgroups (median cut-point), and the prognostic effect of activin A on PFS and overall survival (OS). Results: Baseline activin A levels were determined in 513 patients (71% of 725 BOLERO-2 patients randomized 2:1 to EVE+EXE or EXE). Predictive and prognostic signals are shown in the table below Predictive and prognostic signalsPredictive/PrognosticEnd-pointAct-ivin ATreatmentNEventsMedian PFSHR (95% CI); p valuepredictivePFSHEXE93832.5 (1.5-2.8)-predictivePFSHEVE+EXE1631325.4 (4.1-6.8)0.46 (0.34 - 0.60); <0.0001predictivePFSLEXE89774.2 (2.0 -5.4)-predictivePFSLEVE+EXE1681059.9 (8.1-12.5)0.38 (0.28 - 0.51); <0.0001predictiveOSHEXE936820.1 (13.8-22.6)-predictiveOSHEVE+EXE16312917.7 (15.7-22.3)1.04 (0.78 - 1.40); 0.78predictiveOSLEXE8939NA (34.7-NA)-predictiveOSLEVE+EXE1687241.4 (36.4-NA)1.02 (0.69 - 1.50); 0.93prognosticPFSH 2562154.1 (2.9-4.2)-prognosticPFSL 2571826.9 (6.7-8.5)0.54 (0.45 - 0.66); <0.0001prognosticOSH 25619718.0 (16.5-21.1)-prognosticOSL 25711142.3 (38.5-NA)0.34 (0.27 - 0.42); <0.0001 . In multivariate analysis (including sensitivity to prior hormone therapy and visceral disease), activin A remained a significant independent prognostic factor for PFS and OS [HR 0.57 (0.46-0.69) and 0.34 (0.27-0.43), respectively]. Conclusions: Higher serum activin A was strongly associated with shorter PFS and OS in HR+/HER2- mBC patients. Everolimus was efficacious regardless of serum activin A level. These results are similar to our previous studies in phase 3 trials of letrozole-tamoxifen (Novartis P025), and HER2-targeted therapy, lapatinib vs trastuzmab (CCTG MA.31): pretreatment serum activin A was prognostic for outcome, but was not a predictive factor for treatment arm selection. Citation Format: Ali SM, Chen D, Ali A, Krecko L, Leitzel K, Vasekar M, Nagabhairu V, Marks E, Polimera H, Richardson A, May M, He W, Patel P, Lavin M, Hofsess S, Sweetman R, Hortobagyi G, Baselga J, Lipton A. Serum activin A and outcomes in HR+ /HER2- metastatic breast cancer patients treated with everolimus: Results from BOLERO-2 [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 P1-07-09.

Abstract 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<0.0001); higher CAIX (>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<0.0001) was associated with significantly shorter PFS, along with treatment arm, prior adjuvant anthracyclines, and higher central EGFR status. In multivariate analysis for OS: higher continuous activin A (HR=85.9, with Box-Cox transformation, P<0.0001) was associated with significantly shorter OS, along with treatment arm and higher central EGFR status. The interaction terms of serum biomarkers with treatment were not significant. Elevated serum activin A was also significant at the median cutpoint for PFS (HR 1.79, p=0.0002) and OS (HR 2.39, p=0.006) in multivariate analysis. 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.

617 Background: 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 HER2, CA IX, and TIMP-1. 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 for HER2; 506 pg/ml for CAIX; 454 pg/ml for TIMP-1), 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 HER2 (>median; >15; >30; or >100 ng/ml; p=0.05-0.002); higher CAIX (>median; >506 pg/ml; p=0.02; p=0.001); and higher TIMP-1 (>median; >454 pg/ml; p=0.001; p=0.02) had worse univariate PFS. In multivariate analysis, higher continuous TIMP-1 was associated with significantly worse PFS: HR=1.001 (95% CI=1.000-1.002; p=0.004). Continuous serum HER2 and CAIX were not significantly associated with PFS. HER2 of 15 ng/ml or higher had shorter PFS (p=0.02); higher categorical CAIX had worse PFS (p=0.01-0.08). The interaction terms of HER2, CAIX, and TIMP-1 with treatment were not significant. Multivariate PFS categorical serum results (Table). Conclusions: Higher levels of serum TIMP-1, CAIX, and HER2 were significant prognostic biomarkers of shorter PFS. No serum biomarker was predictive of differential response to lapatinib vs. trastuzumab. Evaluation of TIMP-1 and CAIX targeted therapy in addition to HER2 targeted therapy is warranted in patients with elevated serum levels of these biomarkers. p-value HR Lower CI Higher CI LTax vs TTax 0.001 1.58 1.20 2.06 Adjuvant anthracyclines 0.011 1.58 1.11 2.25 Adjuvant other therapy 0.043 3.88 1.04 14.41 EGFR (% stain) 0.012 1.01 1.001 1.01 Serum HER2 (>15 vs <15 ng/ml) 0.023 1.51 1.06 2.15 Serum CAIX (>506 vs <506 pg/ml) 0.005 1.54 1.14 2.08 *DH and JH contributed equally.