In a groundbreaking phase 2 trial at Memorial Sloan Kettering Cancer Center (MSK), all 12 patients with locally advanced rectal cancer achieved complete remission using the immunotherapy drug dostarlimab alone. Tumors vanished, undetectable by physical exam, endoscopy, PET, or MRI scans. Findings published in the New England Journal of Medicine.
Colorectal cancer ranks as one of the most common cancers worldwide, affecting both men and women. Rectal cancer comprises about 40% of cases, with approximately 10,000 new diagnoses each year in France. Most occur after age 60. The rectum forms the final segment of the digestive tract.
For stage 2 and beyond, surgery remains the cornerstone treatment, often combined with chemotherapy, radiation, or chemoradiotherapy. Five-year survival stands at 63%. As experts seek innovative therapies to improve outcomes, this trial offers new hope.
MSK researchers conducted this small study to potentially spare patients the severe side effects of proctectomy, such as permanent nerve damage and dysfunctions in bowel, bladder, and sexual function.
Building on prior success with pembrolizumab—a similar checkpoint inhibitor—for metastatic colorectal cancers deficient in mismatch repair (dMMR), the team tested dostarlimab. These dMMR tumors resist chemo and radiation because faulty DNA repair enzymes allow genetic errors to accumulate, driving cancer growth.
The trial enrolled 12 patients with non-metastatic, dMMR rectal cancer. Each received 500 mg of dostarlimab every three weeks for six months.
Expectations were modest—most would still need chemo, radiation, and surgery. Yet, all 12 saw complete tumor disappearance with dostarlimab monotherapy, confirmed undetectable by exam, endoscopy, PET, and MRI.
Over two years of follow-up, no patient required further therapy, and zero cases of progression or recurrence occurred. "I believe this is the first time in the history of cancer that every single patient in a trial achieved remission," stated lead investigator Dr. Luis Alberto Diaz, Jr.
While early and limited to dMMR rectal cancer, these results from a top-tier institution like MSK are profoundly promising and warrant larger studies before altering standard care.
