A randomized phase II clinical trial of talazoparib maintenance therapy in patients with triple-negative breast cancer who showed platinum-sensitivity on first- or second-line platinum-based chemotherapy: KCSG BR21-10.
Authors: Sohn Joohyuk , Kim Min Hwan , Kim Gun Min , Kim Jee Hung , Kim Han Jo , LEE JIEUN , Moon Yong Wha , Ahn Hee Kyung , Kim Hee Jun , Shin Seong-Hoon , Lee Moon Hee , Lee Kyoung Eun , Won Hye Sung , Kang Seok Yun , Lee Keun Seok , Park Kyong Hwa 
Published: June 2023

TPS1132 Background: A potent PARP inhibitor, talazoparib, demonstrated superior clinical activity compared to standard chemotherapy in germline BRCA1/2-mutant advanced breast cancer patients. However, the role of talazoparib treatment in BRCA1/2 wild-type triple-negative breast cancer (TNBC) patients remains undefined, although high incidence of homologous recombination deficiency (HRD) is one of the major characteristics of the TNBC. Previous studies indicated clinical responsiveness to platinum agents is a useful surrogate for HRD that may predict favorable PARP inhibitor response. Here, we present a phase II study to test talazoparib maintenance therapy in germline BRCA1/2 mutation unselected advanced TNBC patients after platinum-based chemotherapy. Methods: The KCSG BR21-10 study (NCT04755868) is a randomized double-blind placebo-controlled phase II clinical trial of talazoparib maintenance therapy in metastatic TNBC patients whose tumor showed platinum-sensitivity to first- or second-line platinum-based chemotherapy. The criteria for platinum-sensitivity were set as follows: remaining complete response (CR), partial response (PR), or stable disease (SD) after 6 to 9 tri-weekly doses or 18 to 27 weekly doses of platinum-based chemotherapy. The eligible TNBC patients are enrolled to the trial after completion of platinum-based therapy and 1:1 randomized to receive talazoparib (once daily 1.0 mg) or placebo maintenance therapy. The patient with any germline BRCA1/2 mutation status is eligible, and randomization stratification factors include line of platinum-based chemotherapy, response to platinum-based chemotherapy, and germline BRCA1/2 mutation status. The talazoparib/placebo maintenance treatment is initiated within 8 weeks after the last platinum chemotherapy. At the time of progression of disease, unblinding can be performed and patients in placebo arm may be eligible for crossover to talazoparib single treatment. The primary endpoint is progression-free survival (PFS) after randomization by RECIST 1.1, and the key secondary endpoints are overall survival, PFS2, objective response rate, adverse events by CTCAE 5.0 criteria, and quality of life. We also planned exploratory study to find predictive biomarker by tumor tissue and blood analysis. The median PFS from the randomization is expected to be 3 months in the placebo maintenance arm and we expect that talazoparib maintenance will improve PFS with hazard ratio of 0.65. It is predicted that a total of 206 patients (103 patients in each arm) are required with the α of 0.05 and power of 0.8 (1-β) by two-sided test, considering monthly 3% dropout rate. Currently, 23 of planned 206 patients have been enrolled. Clinical trial information: NCT04755868 .