Scientists are hailing the results of a small clinical trial as groundbreaking after a single immunotherapy drug made all participants’ rectal cancer, usually treated with chemotherapy, radiation and surgery, disappear after six months.
All of the participants had stage 2 or 3 rectal adenocarcinoma (meaning the cancer had reached the lymph nodes but had not metastasized) with a specific mutation that is particularly sensitive to chemotherapy. They received the monoclonal antibody dostarlimab intravenously every three weeks for six months, a total of nine cycles.
Rectal cancer tumors disappeared for all 14 patients who completed treatment—a complete clinical remission. The findings were published in the New England Journal of Medicine by researchers at Memorial Sloan Kettering (MSK) Cancer Center in New York City.
Despite the small sample size, the results are promising.
“That’s 100% of the patients. We never, ever say that about cancer treatments,” Dr. Natalie Azar, a medical contributor for NBC News, said Wednesday, calling the findings “unprecedented.”
The standard of care for this type of cancer is usually chemotherapy, radiation, and surgery. “As you can imagine, (these) leave people with significant disability, and only about 25% of those people will have a clinical remission,” Azar said.
For comparison, the researchers found that the most common side effects of dostarlimab were rash, itching, fatigue, and nausea. “It doesn’t sound like fun, but it’s certainly manageable and not life-threatening,” Azar said.
Dostarlimab, manufactured 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 cancer immunotherapy work?
Immunotherapy works differently than traditional cancer treatments.
“Basically, it’s about harnessing the power of your own immune system to kill cancer cells,” Azar said, unlike chemotherapy, which kills cancer cells but also “lots of good stuff.” 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 that researchers have studied the use of dostarlimab alone to treat this subgroup of rectal cancer patients. “Not all immunotherapies are so dramatically successful,” Azar stressed.
The MSK researchers call this new approach “immunoablative” therapy, which means the immunotherapy is replacing the surgery, chemotherapy and radiation that would otherwise be used to remove the cancer.
In theory, any type of cancer that has the same mutation as MSK patients, also known as mismatch repair deficient (MMRd) cancer, would be “suitable” for this type of immunotherapy, Azar said. Unfortunately, only 5 percent to 10 percent of people with rectal cancer have the mutation that dostarlimab targets, he added.
The researchers are also studying the drug in early-stage pancreatic cancer, one of the deadliest 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 of big cities. But the findings remain a reminder of how clinical trials can change the lives of 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 an immunotherapy clinical trial.
“Ask those questions. Don’t wait,” Azar said.