TESARO Initiates Registrational Development Program for Anti-PD-1 Antibody TSR-042

TESARO an oncology-focused biopharmaceutical company, announced that following the recent identification of a fixed dose and patient-centric dosing schedule, the ongoing clinical trial of TSR-042 has been expanded to enroll patients with metastatic microsatellite instability high (MSI-H) endometrial cancer who have progressed following one or two prior chemotherapy treatments. During the first 12 weeks of treatment, TSR-042 is administered once every three weeks, followed by a single dose administration every six weeks until disease progression. The intent of this study is to support a request for accelerated approval and Biologics License Application (BLA) submission to the U.S. Food and Drug Administration (FDA). The primary endpoints of this trial are overall response rate (ORR) and duration of response, and secondary endpoints include disease control rate, progression free survival (PFS), and overall survival (OS). The addition of cohorts for patients with other tumor types is also planned. This is the first clinical development program within a broader plan that includes potential label expansion trials of TSR-042 in multiple cancers in combination with ZEJULA, TSR-022, TESARO’s anti-TIM-3 antibody, and TSR-033, TESARO’s anti-LAG-3 antibody.

“TSR-042 was the first antibody from our immuno-oncology portfolio to enter clinical trials, and following identification of a fixed dose and schedule, we are pleased to be advancing TSR-042 into a registration program,” said Mary Lynne Hedley, Ph.D., President and COO of TESARO. “With the recent approval of ZEJULA in the U.S., the initiation of this development program furthers our commitment to women with gynecologic tumors, including ovarian, fallopian tube, and peritoneal cancer. We intend to continue our efforts with future combination studies of TSR-042 and ZEJULA, and to someday eliminate these terrible diseases and benefit women who were until recently largely underserved by new therapeutic options.”

About TSR-042

TSR-042 is a monoclonal antibody targeting PD-1 and was developed as part of the collaboration between TESARO and AnaptysBio, Inc. This collaboration was initiated in March of 2014, and is focused on the development of monospecific antibody drugs targeting PD-1, TIM-3 (TSR-022), and LAG-3 (TSR-033), in addition to a bi-specific antibody drug candidate targeting PD-1/LAG-3.

About Endometrial Cancer
Endometrial cancer is the most common type of uterine cancer, accounting for more than 95 percent of cases. Endometrial cancer develops in the lining of the uterus, called the endometrium. The annual number of new cases of endometrial cancer is estimated at 325,000 worldwide. The most common histologic form is endometrioid adenocarcinoma originating in the glandular tissue, which represents about 75-80% of diagnosed cases. In 2017, SEER estimates 61,380 patients will be diagnosed with endometrial cancer, with approximately 30% or 18,414 being stage III/IV patients. Based on genomic characterization studies of endometrial cancer, 20-25% of patients have tumors with a microsatellite instability phenotype (MSI-H).  Microsatellite instability arises from a failure to repair replication-associated errors due to a defective DNA mismatch repair system. This failure allows persistence of mismatch mutations all over the genome, but especially in regions of repetitive DNA known as microsatellites, leading to increased mutational load that has been demonstrated to improve responses to anti-PD-1 therapies.