A modest clinical trial at Memorial Sloan Kettering Cancer Center discovered that every single rectal cancer patient who got an investigational immunotherapy treatment went into remission.

When the findings came in, one participant, Sascha Roth, was planning to go to Manhattan for weeks of radiation therapy, according to Memorial Sloan Kettering. That's when physicians informed her that she was cancer-free.

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Roth told The New York Times that her family wouldn't believe the news when she told them. 

To date, 14 people have seen the same astounding results. The report was published in the New England Journal of Medicine on Sunday. All of the patients had locally advanced rectal cancer and an uncommon mutation known as mismatch repair deficiency (MMRd).

They were given six months of treatment with dostarlimab, an immunotherapy medicine developed by GlaxoSmithKline, which also helped fund the research. The cancer was gone in all of them — undetected by physical exam, endoscopy, PET scans, or MRI scans, according to the researchers.

The $11,000 per dose drug was given to each patient every 3 weeks for a total of six months. It works by exposing cancer cells to the immune system, allowing it to recognize and eliminate them.

CBS News medical contributor Dr. David Agus explained that the new treatment is a type of "immunotherapy, a treatment that blocks the 'don't eat me' signal on cancer cells enabling the immune system to eliminate them."

"The treatment targets a subtype of rectal cancer that has the DNA repair system not working. When this system isn't working there are more errors in proteins and the immune system recognizes these and kills the cancer cells."

After 6 months or more, patients continued to have no signs of cancer - without the need for the standard treatments of surgery, radiation, and chemotherapy.

Cancer has not returned to any of the patients, and they have remained cancer free for nearly 25 months after the trial came to an end. 

According to Agus, it is "amazing" and almost unheard of to have such results, adding that this "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."

Another unexpected finding from the trial was that none of the individuals experienced major adverse effects.

In an MSK news release, Dr. Andrea Cercek, a medical oncologist and principal investigator in the study, described how usual side effects of radiation and surgery may include fertility, sexual health, and bowel and bladder function, noting that "the implications for quality of life are substantial, especially in those where standard treatment would impact childbearing potential. As the incidence of rectal cancer is rising in young adults, this approach can have a major impact."

Cercek said it was extremely rewarding to receive emails from patients that are reporting keeping all their normal body functions.

Researchers believe that the experiment should now be duplicated in much larger research, and they point out that the current study only included patients with a rare genetic signature in their tumors. However, they believe that witnessing full remission in 100% of people examined is a highly positive early indication.

Dr. Hanna K. Sanoff of the University of North Carolina's Lineberger Comprehensive Cancer Center, who was not involved in the study, believes it is unclear whether the patients were cured.

In an editorial, she wrote, "Very little is known about the duration of time needed to find out whether a clinical complete response to dostarlimab equates to cure" but did note that the preliminary results are a cause "for great optimism."

The trial is intended to involve roughly 30 individuals, providing a more complete picture of how safe and effective dostarlimab is in this population.

According to research co-leader Dr. Luis Diaz Jr., director of MSK's division of solid tumor oncology, "While longer follow-up is needed to assess response duration, this is practice-changing for patients with MMRd locally advanced rectal cancer."