A new experimental drug could be the breakthrough cure against cancer after showing promise in a clinical trial.

Memorial Sloan Kettering Cancer Center conducted a small clinical trial on the immunotherapy drug dostarlimab and found evidence that it could treat rectal cancer patients.

The results were startling since every single rectal cancer patient who received the experimental immunotherapy treatment had their cancer go into remission, as per CBS News.

For the trial, participants got subjected to six months of treatment with dostarlimab, a product of the pharmaceutical company GlaxoSmithKline, which also helped fund the study.

The researchers who conducted the trial said that cancer vanished in all of the 14 patients. The cancer cells were not detected through a physical exam, endoscopy, PET scans, or MRI scans after the trial.

The team noted in their study published Sunday in the New England Journal of Medicine that all of the patients who participated in the trial had rectal cancer in a locally advanced stage and with a rare mutation referred to as mismatch repair deficiency (MMRd).

One trial participant named Sascha Roth opened up about her experience, saying she was about to go to Manhattan to have radiation therapy when she got notified about the results.

Roth told the New York Times that after hearing from the doctors that she was cancer-free, she immediately told her family but “they didn’t believe me.”

Six months or more after the trial, the participants had to do several follow-up tests, and they continued to show no signs of cancer. They didn’t need to have surgery, radiation and chemotherapy.

All of the patients remained cancer-free even if it has already been 25 months since the trial ended for some of them.

“Amazing to have every patient in a clinical trial respond to a drug, almost unheard of,” CBS News medical contributor Dr. David Agus said, adding that the it “speaks to the role of personalized medicine — that is identifying a subtype of cancer for a particular treatment, rather than treating all cancers the same.”

The researchers indicated that, surprisingly, no one suffered serious side effects from the experimental drug.