Experimental Rectal Cancer Drug Eliminates Tumors in Small Trial

A small group of patients with rectal cancer experienced surprising results after taking the experimental drug dostarlimab for six months as part of a clinical trial.

All 14 patients in the trial who completed dostarlimab (brand name Jemperli) treatment and an additional six months of follow-up had no evidence of tumors in biopsies, rectal exams, or advanced imaging scans.

And not one of these patients needed chemotherapy, radiation, or surgery, all of which are often standard treatment for rectal cancers, according to results presented at the annual meeting of the American Society of Clinical Oncology and published in The New England Journal of Medicine (NEJM).

“Surgery and radiation have permanent effects on fertility, sexual health, bowel, and bladder function,” Andrea Cercek, MD, lead author of the NEJM paper and co-director of the Center for Young Onset Colorectal and Gastrointestinal Cancer at Memorial Sloan Kettering Cancer Center, said in a statement.

“The implications for quality of life are substantial, especially in those where standard treatment would impact childbearing potential,” Dr. Cercek added. “As the incidence of rectal cancer is rising in young adults, this approach can have a major impact.”

Dostarlimab is in a family of medicines known as checkpoint inhibitors. These so-called immunotherapy drugs work by silencing proteins that tell the immune system not to attack cancer cells.

Worldwide, colorectal cancers are the third most common type of tumors in men and the second most common among women, according to the Canadian Agency for Drugs and Technologies in Health. Up to about 5 percent of colorectal cancers are what’s known as mismatch repair–deficient, meaning tumors develop because cells lack the ability to correct mistakes that lead to cancer.

All of the patients in the trial had a type mismatch repair–deficient rectal cancer. When they joined the trial, scientists expected to treat these patients with intravenous dostarlimab administered every three weeks for six months, followed by standard chemotherapy, radiation, and surgery.

But so far — with follow-up periods up to 25 months — not one patient has needed these standard treatments or see tumors return. There have also been no serious side effects from dostarlimab; the most common side effects were rash or dermatitis, itchy skin, fatigue, and nausea.

“These results are cause for great optimism,” Hanna Sanoff, MD, MPH, of the Lineberger Comprehensive Cancer Center at the University of North Carolina, Chapel Hill, wrote in an editorial accompanying the trial results in NEJM.

But it’s much too soon to replace standard rectal cancer treatment with dostarlimab, Dr. Sanoff cautioned. That’s because seeing no evidence of tumors six months after the end of treatment isn’t always a good reflection of longer-term prognosis or survival odds.

“Despite these uncertainties, Cercek and colleagues and their patients who agreed to forgo standard treatment for a promising but unknown future with immunotherapy have provided what may be an early glimpse of a revolutionary treatment shift,” Sanoff added.

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