Liem, A

Abstract Background: Neoadjuvant chemotherapy is administered to patients with operable breast cancer to downstage the tumor to allow for less extensive surgery and to provide prognostic information about drug efficacy and risk of disease recurrence. Patients who achieve a pathological complete response (pCR) following neoadjuvant treatment have a more favorable outcome than patients with residual invasive disease. Single-agent poly(ADP-ribose) polymerase (PARP) inhibitors have clinical efficacy in BRCA-mutated breast cancer. Niraparib, a potent and selective PARP1/2 inhibitor, is approved for maintenance treatment of patients with recurrent ovarian cancer and has demonstrated strong antitumor activity in in vivo studies with BRCA1-mutant breast cancer. The objective of this study is to evaluate the antitumor activity of single-agent niraparib in the neoadjuvant treatment of patients with localized, human epidermal growth factor receptor 2 (HER2)-negative, BRCAmut breast cancer. Trial Design: This is an open-label, single-arm pilot study with a target enrollment of 20 evaluable patients. Eligible patients are those ≥18 years old with histologically-confirmed HER2-negative localized breast cancer and either a BRCA1 or BRCA2 mutation (germline or somatic) and no prior anti-cancer therapies for the current malignancy. Patients will receive 200 mg of oral niraparib once daily for 2 months, after which they may either proceed directly to surgery or receive chemotherapy at the discretion of the physician. The primary endpoint is tumor response rate based on the change in tumor volume as measured by breast MRI after 2 months of treatment with niraparib; a response is defined as ≥30% reduction of tumor volume from baseline. Secondary endpoints include pCR rate, tumor response rate based on the change in tumor volume as measured by breast ultrasound, and safety and tolerability. Data will be summarized in a descriptive nature by frequency distributions (number and percentage of patients) for categorical variables and by the mean, median, and standard deviation for continuous variables. Tumor response rate will be tabulated together with its 95% binomial exact confidence interval. Funding: TESARO, Inc., Waltham, MA, USA sponsored the study. Citation Format: Han H, Hamilton E, Irie H, Isakoff S, Jelovac D, Liem A, Liu MC, Milillo A, Nangia J, Page D, Reeves J, Santa-Maria C, Duncan M, Graham JR, Chen J, Dezube BJ, Spring L. Open-label, single-arm study evaluating the antitumor activity and safety of niraparib as neoadjuvant treatment in patients with localized, HER2-negative, BRCA-mutant breast cancer [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 OT3-03-01.