Abstract P3-06-12: Effect of TOP2A and cMYC gene copy number on outcome in a Phase II trial of adjuvant TC (Docetaxel/Cyclophosphamide) plus trastuzumab (HER TC) in HER2-positive early stage breast cancer

Introduction: Approximately one-third of HER2+ early stage breast cancer (ESBC) patients have TOP2A-amplified breast cancer, the subpopulation known to benefit from anthracycline use (Press et al, JCO 2011). Data are needed to evaluate whether outcomes in ESBC patients treated with nonanthracycline-based regimens like docetaxel and cyclophosphamide + trastuzumab (HER TC) are affected by TOP2A or cMYC gene copy number. Methods: This was an open-label, phase II study of HER TC in HER2+ breast cancer patients. Outcome data have been previously reported (Jones et al, SABCS 2011, PD07-03). Tissue was collected to review HER2, cMYC, and TOP2A gene copy number at a central reference laboratory. HER2, cMYC, and TOP2A amplification was defined as FISH ratio >2, and deletion was defined as FISH ratio 2 IV and C 600mg/m 2 IV, plus weekly H 4mg/kg IV ( loading dose) and 2mg/kg IV thereafter for a total of 4 cycles. After 4 cycles of TC+H, patients continued on H for 1 year on a 3-week schedule. The primary endpoint was disease-free survival (DFS) at 2 years with continued follow-up for 3 years. Secondary endpoints were overall survival (OS) and safety. Results: 493 patients with HER2+ ESBC were enrolled. From the 493 patients, 438 (89%) tissue samples were available and analyzed at Caris Diagnostics (Phoenix, AZ) to test for TOP2A, cMYC, and HER2 gene copy number by FISH. HER2 status was confirmed as positive in 87% of samples. Results for TOP2A, cMYC, and HER2 were generated in 438, 436, and 438 samples, respectively. TOP2A was classified as amplified in 43%, normal in 30%, deleted in 27%. cMYC was classified as amplified in 99(23%), normal in 246(56%), and deleted in 91(21%). Three-year DFS and OS in TOP2A and cMYC status as well as ER and Nodal status are depicted in Table 1. Multivariate analyses of age, nodal status, ER status, and gene expression shown below in Table 2 indicate that neither cMYC nor TOP2A status had an effect on outcome. Only nodal and ER status affected outcome. Conclusion: Outcome (DFS + OS) in a phase II study of a nonanthracycline regimen (TC) coupled with H was unaffected by cMYC or TOP2A gene copy number status. Only ER and nodal status showed an effect in a multivariate analysis. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-06-12.