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Rectal cancer disappears for every patient in small experimental drug study

100% of rectal cancer patients treated with an experimental immunotherapy drug went into full remission in a small study, researchers said.

Scientists are hailing the results of a small clinical trial as groundbreaking after a single immunotherapy drug caused every participant's rectal cancer — typically treated with chemotherapy, radiation and surgery — to disappear after six months.

Participants all had stage 2 or 3 rectal adenocarcinoma (meaning the cancer had reached the lymph nodes but hadn't metastasized) with a specific mutation that's particularly sensitive to immunotherapy. They received the monoclonal antibody dostarlimab intravenously every three weeks for six months, a total of nine cycles.

The rectal cancer tumors vanished for all 14 patients who completed treatment — a full clinical remission. The findings were published in the New England Journal of Medicine by researchers at New York City’s Memorial Sloan Kettering Cancer Center (MSK).

Despite the tiny sample size, the results are promising.

“That’s 100% of patients. We never, ever say that about cancer treatments,” NBC News medical contributor Dr. Natalie Azar said on TODAY Wednesday, calling the findings "unprecedented."

The standard of care for this kind of cancer is usually chemotherapy, radiation and surgery. “As you can imagine, (these) leave people with significant disability, and only about 25% of those folks will have a clinical remission,” Azar said. 

For comparison, researchers found the most common side effects of dostarlimab were rash, itching, fatigue and nausea. “It doesn’t sound fun, but certainly manageable and not life-threatening," Azar said.

Dostarlimab, made by GlaxoSmithKline and also known by its brand name Jemperli, was first approved by the FDA in April 2021 to treat endometrial cancer in adults.

How does immunotherapy for cancer work? 

Immunotherapy works differently from traditional cancer treatments.

“It’s basically harnessing the power of your own immune system to kill cancer cells,” Azar said, unlike chemotherapy, which kills cancer cells but also "a lot of good things." Dostarlimab is a type of drug called a checkpoint inhibitor, which has been used to treat cancer in the past.

However, this trial was the first time researchers were studying the use of dostarlimab alone to treat this subset of rectal cancer patients. “Not all immunotherapy is this dramatically successful,” Azar stressed.

MSK researchers are calling this new approach “immunoablative” therapy, which means immunotherapy is replacing the surgery, chemotherapy and radiation that would otherwise be used to remove cancer.

In theory, any type of cancer that has the same mutation as the MSK patients, also known as mismatch repair-deficient (MMRd) cancer, would be "amenable" to this type of immunotherapy, Azar said. Unfortunately, only 5 to 10% of people with rectal cancer have the mutation targeted by dostarlimab, she added.

Researchers are also studying the drug in early-stage pancreatic cancer, one of the most deadly types of cancer. Other types of cancer that have this mutation include gastrointestinal, breast, prostate, bladder and thyroid.

Azar noted that the drug needs to be studied in more diverse patient populations in settings outside major cities. But the findings are still a reminder of how life-changing clinical trials can be for individual patients and their families.

If you or a loved one has been diagnosed with cancer, she recommended asking your doctor if you have a type of cancer that could benefit from immunotherapy clinical trial.

"Ask those question. Don't wait," Azar said.