A small study could have a big impact on treating cancer.

The results are preliminary and much more study is needed, but a cancer drug has eliminated cancer in 12 patients so far without chemotherapy or surgery.

The trial led by doctors at New York’s Memorial Sloan Kettering Cancer Center studied the treatment of rectal cancer patients who took dostarlimab. The study was reported over the weekend in the New England Journal of Medicine and the New York Times.

All 12 patients are in complete remission. They’ve experienced no significant side effects and now have no trace of cancer in their bodies. None of the patients required chemotherapy, surgery or radiation treatment.

Some of the patients have remained cancer-free more than two years.

All patients participating in the trial had stage 2 or 3 rectal tumors of a specific type. They were given dostarlimab intravenously every three weeks over a six-month period.

Oncologist Dr. Andrea Cercek approached the study with two goals: preventing cancer cells from masking themselves from the body’s immune system and avoiding the toxicity often associated with treating rectal cancer.

Cercek noted that radiation and chemotherapy treatments can be particularly hard on patients, especially those with rectal cancer. She and her colleague, Dr. Luis Diaz, wanted to pursue an immunotherapy solution.

They aimed to shrink tumors without radiation or chemotherapy.

Dostarlimab is a monoclonal antibody treatment designed to combat cancer cells’ ability to mask themselves from the body’s immune system. This allows immune cells to recognize and attack the cancer cells.

The study planned to have patients go through the treatment and then have standard chemotherapy and surgery. However, the patients did not require the additional treatments.

All 12 patients have been cancer-free for between 6 and 25 months, according to the study. Scans have shown no signs of the tumors. There have been no recurrences of cancer–the cancer effectively disappeared.

“The most exciting part of this is that every single one of our patients has only needed immunotherapy. We haven’t radiated anybody, and we haven’t put anybody through surgery,” Cercek said. “They have preserved normal bowel function, bladder function, sexual function, fertility. Women have their uterus and ovaries. It’s remarkable.”

The doctors acknowledge the sample size is extremely small, however, they’re working to adapt the treatment to other types of cancer, such as stomach, prostate and pancreatic cancers.