Abstract P2-08-19: Exploratory biomarker analyses of FAIRLANE, a double-blind placebo (PBO)-controlled randomized phase II trial of neoadjuvant ipatasertib (IPAT) + paclitaxel (PAC) for early triple-negative breast cancer (TNBC)

Abstract

Abstract Background: The oral AKT inhibitor IPAT is being evaluated in cancers with a high prevalence of PI3K/AKT pathway activation. In the PBO-controlled randomized phase II FAIRLANE trial (NCT02301988), adding IPAT to PAC as neoadjuvant therapy for TNBC led to a numerical increase in pathologic complete response (pCR) in unselected patients (17.1% vs 13.3%), with a greater treatment effect in patients with PIK3CA/AKT1/PTEN-altered tumors (17.9% vs 11.8%). The addition of IPAT also led to an increase in complete response (CR) by MRI (27.6% vs 13.3%) that was enhanced in patients with PIK3CA/AKT1/PTEN-altered tumors (39.3% vs 8.8%) [Oliveira, AACR 2018]. We report an exploratory analysis performed to provide better understanding of potential biomarkers for response. Methods: Pretreatment tumor samples were evaluated for genomic alterations using the FoundationOne® (Foundation Medicine) assay (n=144) and gene expression by RNA-Seq (n=92). Samples were classified into TNBC subtypes based on the method developed by Lehmann and Pietenpol [Lehmann, J Clin Invest 2011]. Tumor-infiltrating lymphocytes (TILs) were quantified using the Salgado method [Salgado, Ann Oncol 2015] (n=135). Results: Of 62 patients (43%) with PIK3CA/AKT1/PTEN-altered tumors, 21 had an activating mutation in PIK3CA or AKT1 and 47 had an alteration in PTEN (6 [3 in each arm] had both PIK3CA mutation and PTEN alteration). Although only 3 patients with PIK3CA/AKT1-mutant tumors achieved a pCR, there was an increased rate of MRI CR with the addition of IPAT to PAC [Table]. In patients with PTEN alterations, both pCR rate and MRI CR rate were increased with IPAT. In patients treated with PBO + PAC, all 4 pCR patients evaluable by RNA-Seq were of the immunomodulatory (IM) subtype. However, in the IPAT + PAC arm, pCRs were also seen in patients with basal-like 1 (BL-1), mesenchymal (M), and mesenchymal stem-like (MSL) subtypes. Consistent with this observation, in the PBO + PAC arm, samples from patients achieving a pCR had significantly higher levels of stromal TILs than those from patients who did not have a pCR, while no difference was observed in the IPAT + PAC arm. Response, n (%)PIK3CA/AKT mutation (n=21)PTEN alteration (n=47) IPAT + PAC (n=11)PBO + PAC (n=10)IPAT + PAC (n=21)PBO + PAC (n=26)pCR1 (9%)2 (20%)4 (19%)3 (12%)CR by MRI5 (45%)1 (10%)8 (38%)2 (8%) Conclusions: This retrospective exploratory biomarker analysis of the phase II FAIRLANE trial of neoadjuvant IPAT for TNBC provides insight into the potential heterogeneity of response and resistance to taxane therapy. The results also hint that response to PAC alone is dependent on baseline immune infiltration and that this dependency might be relieved with the addition of AKT inhibition. Citation Format: Wongchenko MJ, Oliveira M, Saura C, Nuciforo P, Calvo I, Andersen J, Passos Coelho JI, Gil Gil M, Bermejo B, Patt DA, Ciruelos E, Singel SM, Maslyar DJ, Xu N, de la Peña L, Baselga J, Gendreau S, Isakoff SJ. Exploratory biomarker analyses of FAIRLANE, a double-blind placebo (PBO)-controlled randomized phase II trial of neoadjuvant ipatasertib (IPAT) + paclitaxel (PAC) for early triple-negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-08-19.