Dostarlimab made headlines earlier this month after news broke that every patient with a certain type of rectal cancer was put into remission after using the cancer drug in a clinical trial.
The trial was small—it involved just 18 people and only 12 completed the treatment—but the results were exciting. The researchers found that, after taking dostarlimab every three weeks for six months, all patients with mismatch repair-deficient stage II or III rectal adenocarcinoma had “no evidence of tumor” on MRI or other tests.
“At the time of this report, no patients had received chemoradiotherapy or undergone surgery, and no cases of progression or recurrence had been reported during follow-up,” which was between six to 25 months, the researchers wrote.
Doctors and rectal cancer patients alike are wondering if these impressive results will be replicated in larger trials. But it’s important to note that dostarlimab isn’t a new drug and is already being used to fight cancer. It’s currently approved by the Food and Drug Administration (FDA) for a specific form of endometrial cancer and for some solid tumors.
So, what else can dostarlimab treat and how does this drug work? Here’s what you need to know.
Dostarlimab is a type of immunotherapy in a class of drugs known as PD-1 inhibitors, Jamie Alan, PharmD, PhD, associate professor of pharmacology and toxicology at Michigan State University, told Verywell.
“This blocks the PD-1–programmed death receptor-1—which is involved in the immune response,” she said. “It is the immune system’s job to destroy foreign material and cells, including cancer cells.”
Cancerous tumors can express this PD-1 receptor, which “hides” the tumor from the immune system. According to Alan, dostarlimab will block this receptor, allowing the immune system to recognize, attack, and destroy the tumor.
Dostarlimab is administered via intravenous (IV) infusion, and there are similar drugs out there.
“The drug is in the same category as Opdivo (nivolumab) or Keytruda, (pembrolizumab),” Namrata Vijayvergia, MD, assistant chief of gastrointestinal medical oncology at Fox Chase Cancer Center in Philadelphia, told Verywell.
Currently, dostarlimab is only FDA-approved to treat mismatch repair deficient (dMMR) recurrent or advanced endometrial cancer and dMMR solid tumors. But it’s also part of 20 other clinical trials, including several for breast cancer. That volume is not shocking, Padmanee Sharma, MD, PhD, professor of genitourinary medical oncology and immunology, and scientific director of the James P. Allison Institute at MD Anderson Cancer Center, told Verywell.
“Because it’s an immunotherapy drug, it’s not specific for tumor types,” she said. This means the drug could technically be used to treat a range of cancers. However, GSK, the maker of dostarlimab, has only completed clinical trials on patients with endometrial cancer and sought FDA approval for that specific indication.
Sharma points out that there are several different medications in this class and that they all block the same biologic pathway.
“It’s just that different companies have done their clinical trials on different [forms of cancer],” she said.
Ibrahim Halil Sahin, MD, a gastrointestinal oncologist at Moffitt Cancer Center, told Verywell that the clinical trial that showed impressive results for dostarlimab was only for a very specific type of rectal cancer, and that’s been confusing for his patients. However, it doesn’t mean it won’t be effective in other forms of cancer—it just hasn’t been tested yet.
“Studies are looking into the benefits of dostarlimab and other PD-1 inhibitors in different patient populations,” he said. “Could it turn out to be an effective anti-cancer drug? Maybe.”
Sahin also stressed that dostarlimab is “not any different from other PD-1 inhibitors.” He says it’s very likely that other drugs in this same class will have similar successful results.
“The future of immunotherapy in cancer care is bright,” Vijayvergia said. “We need to find ways to make immunotherapy effective in more types of tumors rather than just MMR deficient and these studies are trying to study these exact same questions.”
The immunotherapy drug dostarlimab showed impressive results in a small clinical trial, but the trial was small and the type of cancer was very specific. More research is needed to see if the results can be replicated in other forms of cancer and with a larger patient population.