Abstract P3-07-13: Homologous recombination deficiency (HRD) as a predictive biomarker of response to preoperative systemic therapy (PST) in TBCRC008 comprising a platinum in HER2-negative primary operable breast cancer

Abstract

Abstract Background: Biomarkers to predict response to platinum-based therapy in early breast cancer are needed. HRD is a promising predictor of response to DNA damaging agents, such as platinums. We hypothesized that HRD (high HRD score ≥ 42 and/or tumor BRCA [tBRCA] mutation) would predict pathological complete response (pCR) in patients with HER2-negative early breast cancer treated with PST comprising a platinum, regardless of estrogen receptor (ER) status. Methods: TBCRC008 was a multicenter placebo-controlled trial that investigated pCR (no invasive cancer in breast/axilla) following 12 weeks of preoperative carboplatin and albumin-bound paclitaxel with or without vorinostat in patients with ER-positive or triple-negative breast cancer (TNBC) (Connolly RM. JNM 2015). The pCR rate was similar in both arms (vorinostat 25.8%, placebo 29%). We performed an exploratory biomarker study correlating baseline tumor biopsy HRD status with pCR. The analysis population included all patients with available HRD and pCR data. We compared the proportion of patients with pCR by HRD status using Fisher's exact test. A subset analysis compared pCR proportions by high (≥42) vs. low (<42) HRD score in those patients who did not have tBRCA mutation. A logistic regression model included HRD status, ER status, treatment arm, tumor grade and use of additional anthracycline-based non-study chemotherapy prior to definitive surgery. Results: HRD status and pCR data were available for 48/62 patients (30 ER-positive, 18 TNBC). Of these, 46% of tumors were HR deficient (n=22/48, 33% ER-positive [10/30], 67% TNBC [12/18]). We observed a significantly higher pCR rate in patients with HR deficiency vs not (50% vs 7.7%, p=0.002) in the overall population. A similar trend was observed in ER-positive (30% vs 5%, p=0.095) and TNBC (66.7% vs 16.7%, p=0.13) patients. There was no significant difference when analyzed by treatment arm (vorinostat vs placebo). In a subgroup analysis (n=40) of patients without tBRCA (25 ER-positive, 15 TNBC), a significantly higher pCR rate was observed in those with high vs low HRD score (64.3% vs 7.7%, p <0.001). After adjusting for ER status, randomized treatment, use of AC treatment, and tumor grade, patients whose tumors exhibited HR deficiency had a greater than 6 fold increase in pCR compared to those without HR deficiency (adjusted odds ratio = 6.76, 95% CI = 0.85-53.99, p=.072). Conclusion: This is the first study to evaluate the predictive role of HRD status in patients with ER-positive, HER2-negative breast cancer treated with platinum-based therapy. Our results also support prior observations that HRD status is a promising predictive biomarker of response to platinum agents in TNBC. Further evaluation of this question is warranted in both TNBC and ER-positive breast cancer. Citation Format: Connolly R, Elkin E, Timms K, Goetz M, Boughey J, Zhang Z, Walsh B, Carpenter J, Storniolo A, Watkins S, Gabrielson E, Hartman A-R, Stearns V. Homologous recombination deficiency (HRD) as a predictive biomarker of response to preoperative systemic therapy (PST) in TBCRC008 comprising a platinum in HER2-negative primary operable breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-13.