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A dozen patients with rectal cancer saw their cancer disappear after taking part in an immunotherapy trial. The small clinical trial, led by researchers from Memorial Sloan Kettering Cancer Center in New York, focused on a subset of patients whose cancer had a specific mutation.

Details of the trial were published in the New England Journal of Medicine. A total of 12 patients completed a six-month course of treatment with dostarlimab. All 12 saw their tumors vanish without need of additional therapies, such as chemotherapy, radiation therapy or surgery. 

“I believe this is the first time this has happened in the history of cancer,” Dr. Luis A. Diaz Jr. of Memorial Sloan Kettering, one of the study authors, told The New York Times.

“What’s really remarkable is this is the first time I know of in solid tumor oncology where we’ve had a 100% complete response, and we’ve completely omitted the normal standard of care,” he added to Stat News.

Dr. Ibrahim Halil Sahin of the Department of Gastrointestinal Oncology at Moffitt Cancer Center said the study has big potential, but results should be taken with a grain of salt.

headshot of Dr. Ibrahim Halil Sahin, Gastrointestinal Oncology Program at Moffitt Cancer Center

Dr. Ibrahim Halil Sahin, Gastrointestinal Oncology Program

“This bottom line is that the results of this study are practice changing, but patients with mismatch repair deficient (MMR-D) rectal cancer only represent a small percentage of all rectal cancer cases,” said Sahin. “Patients with MMR-D only make up about 5-10% of locally advance rectal cancer. In this study, all patients with locally advanced rectal cancer turned out to have complete clinical response. It’s highly promising and also consistent what we observed with these class of drugs for patients with metastatic MMR-D colorectal cancer. However, complete clinical response doesn’t always mean the tumor is completely vanished, but it means it can’t be measured at this stage radiologically and endoscopically. Importantly this means these patients can avoid a surgery that entails removal the rectum and continue with active surveillance.”

Mismatch repair deficient rectal cancer can have mixed results when responding to standard chemotherapy regimens. In the trial, researchers wanted to investigate if immunotherapy alone could beat rectal cancer that had not spread to other tissues.

“I doubt we will see major deviation with an expansion cohort as the biology of MMR-D rectal cancer is consistent with the response we see here in this study,” said Sahin. “The bright side is one agent achieves all that we try to achieve with chemotherapy and chemoradiation for organ preservation for MMR proficient rectal cancer.”

While research is ongoing, investigators say at least 14 patients “and counting” have seen their tumors disappear, with none experiencing significant side effects. There was also no need for further radiation, surgery or chemotherapy, and the cancer has not returned in any of the patients two years later.

“We need to see long term outcomes, but nonetheless this is always something we’re trying to achieve,” said Sahin. “I think this is going to change the way we practice in the future, but the key message is that this is a small subgroup of patients. We still need to address the majority of rectal cancer patients who have MMR proficient disease.”