A clinical trial of immunotherapy delivered remarkable results for a select group of cancer patients with solid tumors in the stomach, rectum, esophagus, and other organs.
In an immunotherapy clinical trial conducted by researchers at Memorial Sloan Kettering Cancer Center in New York, the majority of cancer patients experienced complete tumor disappearance, with no signs of recurrence since.
When patients develop solid tumors in organs such as the stomach, rectum, or esophagus, oncologists have well-established treatment options. However, these treatments often have serious consequences for a patient's quality of life — including major surgeries like bladder or stomach removal, permanent colostomy bags, radiation-induced infertility, and lasting side effects from chemotherapy.
To explore a less invasive solution, a research team at Memorial Sloan Kettering Cancer Center partnered with pharmaceutical company GSK to test a different approach. They enrolled 103 patients, representing the small 2–3% of cancer cases with tumors that are especially responsive to immunotherapy — a type of treatment designed to help the immune system bypass tumor defenses and attack cancer cells.
Although immunotherapy is typically used alongside conventional treatments, this trial — led by Dr. Luis A. Diaz Jr. and Dr. Andrea Cercek — tested the immunotherapy drug dostarlimab on its own.
The outcome was remarkable. Of the 49 patients with rectal cancer, all experienced complete tumor remission, with no recurrence reported even after five years. Among the remaining 54 participants who had other forms of cancer — including tumors in the stomach, esophagus, prostate, endometrium, liver, and urinary tract — 35 also had their cancers disappear entirely.
Only five patients in the study saw their cancer return. Three received more doses of immunotherapy, one had a cancerous lymph node removed, and all four are currently cancer-free. The fifth experienced tumor shrinkage after further treatment.
The results were presented at the American Association for Cancer Research’s annual meeting and published in The New England Journal of Medicine. Dr. Bert Vogelstein, a leading oncologist at Johns Hopkins, described the findings as “groundbreaking.” He noted that earlier stages of the drug's development took place in his lab, and that these outcomes are the result of decades of research stemming from foundational scientific discoveries.
The reason immunotherapy was effective in this study is due to a genetic anomaly in the patients’ tumors called mismatch repair (MMR) mutations. These mutations prevent the cells from repairing DNA damage, leading to abnormal proteins that alert the immune system. Tumors typically block immune responses using a protective barrier, but immunotherapy is able to break through and allow the immune system to eliminate the cancer.
Dr. Michael Overman, a gastrointestinal cancer expert at MD Anderson Cancer Center, believes the study proves that immunotherapy — without surgery, chemo, or radiation — is a sound and logical treatment for certain patients.
However, broader access remains a challenge. Each dose of dostarlimab costs roughly $11,000, and the full course requires nine infusions over six months. Insurance coverage depends on whether the drug is listed in official treatment guidelines. While it is approved for certain uterine cancers with MMR mutations and is now recommended for rectal cancer based on prior research, patients with other cancer types may have difficulty accessing it. Memorial Sloan Kettering is still enrolling qualified patients in its ongoing clinical trial, allowing them to receive the treatment for free.
For some, immunotherapy has been life-changing. Though generally well-tolerated, side effects can include fatigue, rashes, and itching. More serious but rare complications include lung inflammation and encephalitis.
One patient, 71-year-old Maureen Sideris from Amenia, New York, discovered her cancer after struggling to swallow a hamburger. Doctors found a tumor at the junction of her stomach and esophagus. In 2022, she visited Sloan Kettering and was told she would likely need extensive surgery, chemotherapy, and radiation. The surgery might have involved removing part of her stomach and moving her esophagus.
But tests revealed that her tumor had the MMR mutation, qualifying her for the trial. She began treatment in October 2022, and by January, the tumor had completely disappeared. The only lasting side effect she’s experienced is a need for medication to support adrenal gland function — a small price, she said, compared to the invasive treatment she would have faced otherwise.
“It’s been a journey,” she shared. “But I figured I had nothing to lose by trying immunotherapy. Surgery was still an option if it didn’t work.”
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