Small drug trial clears more than a dozen patients of rectal cancer tumours

TORONTO -

All rectal cancer patients in a small clinical trial saw a complete remission after being treated with the experimental drug dostarlimab, according to a new study published in the New England Journal of Medicine.

Researchers at the Memorial Sloan Kettering (MSK) Cancer Centre in New York reported a 100 per cent remission of rectal cancer in the first fourteen patients treated.

Colorectal cancer is the third most common cancer in the U.S. and fourth in Canada. According to the Canadian Cancer Society 24,300 Canadians are expected to be diagnosed with colorectal cancer in 2022; representing 10 per cent of all new cancer cases for the year.

In the trial, patients were treated with the drug every three to six months and would then be treated with standard chemoradiotherapy and surgery if needed. However, none of the patients required chemoradiotherapy or surgery. Additionally, no progression of cancer was reported in any of the patients, as well as no major side effects.

“The most exciting part of this is that every single one of our patients has only needed immunotherapy,” oncologist Dr. Andrea Cercek, lead researcher in the study, said in an MSK blog post.

“They have preserved normal bowel function, bladder function, sexual function, fertility. Women have their uterus and ovaries. It’s remarkable.”

Standard treatments like chemotherapy often pose a risk for life-altering side effects in these patients who were diagnosed with a specific subset of rectal cancer called mismatch repair-deficient (MMrd).

According to the U.S. National Cancer Institute, patients with MMrd have deficient cells that produce many DNA mutations which may lead to cancer, most commonly colorectal cancer.

Cercek explained in a blog post that a type of immunotherapy called a checkpoint inhibitor is able to recognize and attack these cancer cells by releasing immune cells.

“When the brakes are taken off the immune cells, MMRd cells look especially strange because they have so many mutations. So the immune cells attack with much more force,” she said. 

Medical oncologist and professor at the University of British Columbia Dr. Sharlene Gill, who wasn’t involved in the trial, told CTVNews.ca that while the results are exciting, it’s too early to tell how soon this treatment will be made available to more patients.

“As we’ve seen academically in many other studies before, typically it's difficult to change standard of care based on a small study done at a single centre,” she said in a phone interview on Tuesday.

“You generally need a broader patient population that's treated in greater numbers of patients to really have a robust understanding of what the effect will have here.”

Currently, the 14 patients and counting who have had a complete clinical response have had at least a six month follow-up. Gill said once more patients surpass longer follow-ups this will also help in furthering research to help patients undergo less stressful treatments.

“Can we potentially treat patients with less treatments like radiation, chemotherapy and surgery and still achieve a cure? That will require more patients to fully understand that and also longer follow ups. So right now the follow up is still short so this is considered early, but very promising,” she said.