Abstract GS3-02: Invasive disease-free survival and gene expression signatures in CALGB (Alliance) 40601, a randomized phase III neoadjuvant trial of dual HER2-targeting with lapatinib added to chemotherapy plus trastuzumab

Purpose Dual HER2 targeting increases pathologic complete response (pCR) rate to neoadjuvant therapy and improves outcomes in both early and metastatic HER2-positive disease. CALGB 40601 is a randomized phase III trial examining the impact of dual HER2 blockade consisting of trastuzumab (H) and lapatinib (L) added to paclitaxel (T) on pCR, considering tumor and microenvironment molecular features. We previously found that pCR was numerically but not significantly increased with dual therapy, and that tumor molecular subtype and evidence of immune activation significantly and independently affected pCR (Carey et al, JCO 2016). In this secondary analysis, we sought to evaluate the effects of treatment arm and gene expression-defined subgroups on invasive disease free survival (IDFS). Patients and Methods Patients (Pts) with stage II to III HER2-positive breast cancer underwent tumor biopsy followed by random assignment with equal probabilityto paclitaxel plus trastuzumab alone (TH) or with the addition of lapatinib (THL) for 16 weeks before surgery. A paclitaxel plus lapatinib (TL) arm was closed early based on reports of futility from other trials. A secondary endpoint was IDFS, defined as the time from surgery until local or distant recurrence, new primary, or death from any cause, whichever was first. Gene expression signatures were identified by RNA sequencing. Results Between 12/2008 and 2/2012, 305 pts were enrolled. 261 pts had IDFS and gene expression information available (THL, n = 103; TH, n =101; TL, n = 57); there were no significant differences in clinical characteristics between this subset and the entire population. The median IDFS follow-up was 4.6 years with 40 IDFS events having occurred (THL, n=7; TH, n=19; TL, n=14). IDFS was significantly longer in the THL arm compared to standard TH (HR=0.34; 95% CI: 0.14-0.82; p=0.02). IDFS was also significantly longer among pCR than non-pCR pts (HR=0.40; 95% CI: 0.19-0.81; p=0.01), and did not differ by hormone receptor (HR) status, clinical stage, tumor size, race, menopausal status or age. Among gene expression signatures, only immune activation measured by an IgG signature was associated with longer IDFS (HR=0.71; 95% CI: 0.51-0.98; p=0.04); this signature was previously also associated with pCR. Multivariate analysis showed dual therapy (HR=0.35; p=0.02), pCR (HR=0.36; p=0.01), IgG (HR=0.69; p=0.05), and molecular subtype (LumA vs HER2E, HR=0.24, p=0.005) were associated with longer IDFS. A subgroup analysis by hormone receptor status revealed that among pts with HR+ disease, pts with luminal A experienced longer IDFS (HR=0.23; p=0.02) compared to those with luminal B or HER2-enriched molecular subtypes. Conclusion Dual HER2-targeting with lapatinib added to 16 weeks of TH produced significantly longer IDFS than TH alone, despite modest effects on pCR. Similar to pts with HER2-negative disease, pts with luminal A had better IDFS than those with other molecular subtypes. Immune activation as measured by RNA-based signature independently predicted both pCR and IDFS. Support: U10CA180882, U10CA180821, U24CA196171, P50-CA58823, Susan G Komen, BCRF Citation Format: Krop IE, Hillman D, Polley M-Y, Tanioka M, Parker J, Huebner L, Henry NL, Tolaney SM, Dang C, Harris L, Berry DA, Perou CM, Partridge A, Winer EP, Carey LA. Invasive disease-free survival and gene expression signatures in CALGB (Alliance) 40601, a randomized phase III neoadjuvant trial of dual HER2-targeting with lapatinib added to chemotherapy plus trastuzumab [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 GS3-02.