GlaxoSmithKline's Tesaro unit on Tuesday announced preliminary results from the Phase I/II GARNET study, which showed "clinically meaningful and durable response rates" of the PD-1 inhibitor dostarlimab in women with recurrent or advanced endometrial cancer who progressed on or after a platinum-based regimen. Tesaro president Mary Lynne Hedley remarked "we intend to use these and other data from the GARNET study to seek regulatory approval of dostarlimab to potentially address the critical unmet treatment needs of women whose disease has progressed."  

In the study, 125 patients, including 41 microsatellite instability-high (MSI-H) and 79 (microsatellite stable) MSS patients, as well as five patients with an unknown microsatellite instability (MSI) status, were treated with dostarlimab at a dose of 500 mg once every three weeks for four doses followed by 1000 mg once every 6 weeks until disease progression. Study findings, which were presented at the Society for Gynecologic Oncology annual meeting on Women's Cancer, showed that the overall response rate in the full population was 30 percent, including rates of 49 percent and 20 percent in the MSI-H and MSS populations, respectively.  

In addition, the drugmaker noted that the disease control rates in the full, MSI-H and MSS populations were 53 percent, 63 percent and 47 percent, respectively. At the time of data cut-off, 84 percent of responders were continuing treatment, with 89 percent and 49 percent of responders having been on treatment for more than six months and more than one year, respectively. 

The durability of the response was similar between the MSI-H and MSS populations, while the median duration of response has yet to be reached. GlaxoSmithKline noted that further data from the GARNET study will be analysed to support regulatory filing of the experimental therapy for the treatment of endometrial cancer by the end of the year. 

Dostarlimab was developed as part of a collaboration initiated in 2014 between Tesaro and AnaptysBio. Meanwhile, GlaxoSmithKline completed its $5.1-billion acquisition of Tesaro in January. 

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