Immunotherapy Breakthrough Could Help Some Cancer Patients Avoid Surgery and Chemotherapy

• Researchers found that some cancer patients who used a new immunotherapy drug were able to shrink their tumors without undergoing chemotherapy or surgery
• 103 patients participated in the study, and 84 had “all signs of their cancer” disappear
• Researchers said that the immunotherapy drug appeared to only work well with patients who had mismatch repair-deficiency, a unique genetic mutation most often found in patients with colorectal cancer

A new immuno-based treatment could treat tumors without cancer patients undergoing surgery or chemotherapy, according to a new study.

The research, published in The New England Journal of Medicine and announced at the American Association of Cancer Research (AACR) Annual Meeting, suggested that 92% of patients who used the new immunotherapy drug, dostarlimab, to shrink their tumors ,continued to be cancer-free for at least two years.

Treating cancer usually involves a form of immunotherapy alongside chemotherapy and surgery to remove a tumor. However, the new immuno-based treatment would only require a single step — immunotherapy — to treat the cancer by teaching a person’s immune system to recognize and attack cancer cells.

One hundred and three patients participated in the study, 54 with a variety of "solid tumor cancers," including stomach, endometrial and prostate, and 49 with rectal cancer.

Researchers shared in a press release from The Memorial Sloan Kettering Cancer Center that of the 54 patients with a “variety of cancers," 35 had “all signs of their cancer” disappear and were using the immuno-based treatment.

Per the release, Dr. Andrea Cercek said, "Nearly 2 out of 3 patients with types of cancer other than rectal were able to preserve their organs and their quality of life."

“This is a very significant response, and the results were even better than we had hoped,” Dr. Cercek said. “We found that some cancer types responded extremely well to the immunotherapy, including colon and stomach cancer.”

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer, from celebrity news to compelling human interest stories.

Maureen Sideris, a patient who was diagnosed with gastroesophageal junction cancer in 2022 and participated in the study, said that the treatment had worked successfully for her, according to the Memorial Sloan Kettering Cancer Center release.

“My husband, Tommy, and I were preparing for the worst,” she recalled in a statement. “But after being treated with only immunotherapy, I had no evidence of cancer and didn’t have to undergo surgery or chemo or radiation. I felt like I won the lottery!”

Dr. Cerek reported that “20% of non-rectal cancer patients” who still had to undergo surgery “saw lower rates of cancer recurrence." She said this suggests that “even if the effect wasn’t a home run, it helped most patients.” 

As for all 49 patients with rectal cancer who participated in the study, “there was no evidence of cancer after immunotherapy,” according to the Memorial Sloan Kettering Cancer Center release. Researchers said that one patient had a “growth in a lymph node” that was surgically removed but they “kept their rectum.”

However, researchers said that the new treatment comes with its own drawbacks as the immunotherapy drug appeared to only work well with patients who had mismatch repair-deficiency, which means certain cells have mutations when cancer cells separate, according to the National Cancer Institute (NCI). 

Per the NCI, this mutation “is most common” in “colorectal cancer, other types of gastrointestinal cancer, and endometrial cancer" and can also be found in “cancers of the breast, prostate, bladder and thyroid.” The immunotherapy drug works by targeting cells with this mutation, as the immunotherapy drug can more easily target the many mutations, per the study.

“We’re really excited to help more people,” Dr. Cercek said. “And we are already exploring why rectal tissue seems to have such an extraordinary response to immunotherapy and how we can use that knowledge to help with other cancer types.”