GSK announced updated, longer-term results from the phase II supported collaborative study with Memorial Sloan Kettering Cancer Center (MSK) evaluating Jemperli (dostarlimab) as a first-line treatment—as an alternative to surgery—for mismatch repair deficient (dMMR) locally advanced rectal cancer.

The trial showed an unprecedented 100% clinical complete response rate (cCR) in 42 patients who completed treatment with dostarlimab, defined as complete pathologic response or no evidence of tumours as assessed by magnetic resonance imaging, endoscopy and digital rectal exam. In the first 24 patients evaluated, a sustained clinical complete response with a median follow-up of 26.3 months (95% CI: 12.4-50.5) was observed.

Hesham Abdullah, Senior Vice President, Global Head Oncology, R&D, GSK, said: “The data showing no evidence of disease in 42 patients is remarkable. These results bring us one step closer to understanding the potential of dostarlimab in this curative-intent setting for patients with dMMR locally advanced rectal cancer. We look forward to evaluating dostarlimab in certain colorectal cancers in our ongoing AZUR-1 and AZUR-2 registrational studies.”

The current standard-of-care (SoC) for patients with dMMR/microsatellite instability-high (MSI-H) locally advanced rectal cancer is initial treatment with chemotherapy plus radiation followed by surgery to remove the tumour along with portions of the intestine and/or surrounding tissue.1 This results in initial positive outcomes for most patients, but nearly one-third ultimately die from cancer that has spread to other parts of the body (distant metastasis). Additionally, the surgery and chemoradiotherapy associated with SoC can lead to long-term adverse effects that have a significantly negative impact on quality of life, including bowel, urinary and sexual dysfunction, secondary cancers and infertility.

Andrea Cercek, MD, Section Head of Colorectal Cancer and Co-Director of the Center for Young Onset Colorectal and Gastrointestinal Cancer, MSK, and Principal Investigator of the phase II study said: “These findings demonstrate the potential of dostarlimab as a novel approach to treating locally advanced dMMR rectal cancer that leads to durable complete tumour regression without the need for life-altering treatment. As a clinician, I’ve seen firsthand the debilitating impact of standard treatment of dMMR rectal cancer and am thrilled about the potential of dostarlimab in these patients.”

The safety and tolerability profile of dostarlimab was generally consistent with the known safety profile of the agent. No adverse events of grade 3 or higher were reported in this trial.

Dostarlimab is not approved anywhere in the world for the frontline treatment of locally advanced dMMR rectal cancer.