Abstract 4209: First-line doublet chemotherapy for mTNBC: circulating tumor cell analysis of the tnAcity trial

Abstract

Abstract Introduction Circulating tumor cells (CTCs) have been shown to be prognostic in patients (pts) with metastatic breast cancer (MBC) (Pukazhendhi, Gluck, J Carcinog. 2014). The tnAcity trial evaluated the efficacy/safety of 3 chemotherapy combination regimens (nab-P/carboplatin [C], nab-P/gemcitabine [G], or G/C) as first-line treatment for pts with mTNBC. nab-P/C resulted in a significantly longer PFS & numerically higher ORR vs nab-P/G or G/C (Yardley. SABCS 2016; manuscript in process). CTC levels were assessed at baseline (BL) & during treatment to determine correlation with clinical benefit. Methods Pts with pathologically confirmed mTNBC & no prior cytotoxic chemotherapy for MBC received (1:1:1) nab-P 125 mg/m2 with C area under the curve (AUC) 2, nab-P 125 mg/m2 with G 1000 mg/m2, or G 1000 mg/m2 with C AUC 2, all given d1 & 8 q3w. Primary endpoint: investigator-assessed PFS. Secondary endpoints included ORR & OS; CTC enumeration was a prespecified exploratory objective. CTC levels, assessed (CELLSEARCH®) at BL & start of cycles 3 & 5 (post-BL), were grouped as follows: 0 CTCs/7.5 mL blood at BL (−−), ≥ 1 CTCs/7.5 mL blood at BL & post-BL (++), & ≥ 1 CTCs/7.5 mL blood at BL & clearance of CTCs in ≥ 1 post-BL measurement (+−). Results In total, 126 pts were included: 48, 24, & 54 in the −−, ++, & +− groups, respectively. Mean BL CTC levels for the ++ & +− groups were 55 & 66 CTCs/7.5 mL blood. Pts with BL CTCs of ≥ 1 vs 0 had numerically similar median PFS (7.0 vs 5.9 mo; HR 1.45 [95% CI 0.93 - 2.25]) & OS (15.0 vs 16.0 mo; HR 0.90 [95% CI 0.57 - 1.42]) & higher ORR (64% vs 44%). Mean cycle 3 & 5 CTC levels in the ++ group were 17 & 111 CTCs/7.5 mL blood. Pts in the −− & +− groups had longer PFS vs the ++ group (median 5.9, 8.5, & 4.7 months). Similar improvements in OS & ORR were noted (Table). Conclusions Absence of CTCs at BL & during treatment & clearance of CTCs from BL at least once during treatment were generally associated with improved efficacy outcomes in pts with mTNBC treated with combination chemotherapy. Table. Outcomes by Change in CTC Level from BaselineGroupOutcome−− n = 48+− n = 54++ n = 24PFS, median, mo HR (95% CI)5.9 0.60 (0.34-1.06)a8.5 0.30 (0.17-0.54)a4.7OS, median, mo HR (95% CI)16.0 0.40 (0.22-0.73)a17.8 0.35 (0.20-0.62)a9.8ORR, %43.879.629.2CR6.316.74.2PR37.563.025.0SD35.420.454.2PD16.7—16.7NE4.2——CR, complete response; HR, hazard ratio; NE, not evaluable; ORR, overall response rate; OS, overall survival; PD, progressive disease; PFS, progression-free survival; PR, partial response; SD, stable disease. a vs ++ group. Citation Format: Minetta C. Liu, Wolfgang Janni, Vassilis Georgoulias, Denise A. Yardley, Nadia Harbeck, Xin Wei, Desmond McGovern, Robert Beck. First-line doublet chemotherapy for mTNBC: circulating tumor cell analysis of the tnAcity trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4209.