Doctors have been left astonished after an experimental cancer drug caused every patient in a trial to enter remission.
The drug dostarlimab appeared to cure every patient during a clinical trial at the Memorial Sloan Kettering Cancer Center (MSKCC) in New York.
The cancer drug was given to 18 people with a type of rectal cancer every three weeks for six months.
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And although scientists say it is too early to tell if the patients are totally cured, the drug seemed to remove rectal cancer with minimal side effects.
After having had the new treatment, all the patients discovered that their cancer had disappeared on physical examination, endoscopy, or PET and MRI scans, said the MSKCC researchers.
"I believe this is the first time this has happened in the history of cancer," said Dr Luis Diaz, one of the lead authors of the paper and an oncologist at MSKCC, according to the New York Times.
"It's really exciting. I think this is a great step forward for patients."
He added that he thought this was just the "tip of the iceberg".
Dr Hanna Sanoff of the University of North Carolina's Lineberger Comprehensive Cancer Center wasn't involved in the study but is excited by the results.
"Absolutely. I mean, I am incredibly optimistic.... we have never seen anything work in 100% of people in cancer medicine," she said, reported NPR.org.
"This drug is one of a class of drugs called immune checkpoint inhibitors. And these are immunotherapy medicines that work not by directly attacking the cancer itself but actually getting a person's immune system to essentially do the work.
"And these are drugs that have been around in melanoma and other cancers for quite a while but really have not been part of the routine care of colorectal cancers until fairly recently."
Dr Sanoff says that the next stage is to have wider testing of the drug.
"What I'd really like us to do is get a bigger trial where this drug is used in a much more diverse setting to understand what the real, true response rate's going to be," she said.
"It's not going to end up being 100%. I hope I bite my tongue on that in the future, but I can't imagine it will be 100%. And so when we see what the true response rate is, that's when I think we can really do this all the time."
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