An experimental drug appeared to clear every patient of rectal cancer with minimal side effects in an unprecedented study, but oncologists say it's too early to be sure that they're cured.
Dr. Alan P. Venook, a colorectal cancer specialist at the University of California, San Francisco, told the New York Times that complete remission in every single patient was "unheard-of".
The drug, called dostarlimab, was given to 12 people with a specific type of rectal cancer every three weeks for six months in a small study at the Memorial Sloan Kettering Cancer Center in New York.
After the course of treatment, cancer was undetectable on physical exam, endoscopy, PET, and MRI scans for every person, the researchers from MSKCC said in a presentation at the annual meeting of the American Society of Clinical Oncology on Sunday
The participants didn't need any other treatment for up to a year, on average, and there were no side effects bad enough to impact day-to-day activities, the researchers said.
Dr. Alan P. Venook, a colorectal cancer specialist at the University of California, San Francisco, who was not involved with the study, told the New York Times that complete remission in every single patient was "unheard-of".
Dr. Andrea Cercek, an oncologist at MSKCC and a study co-author, said there were "a lot of happy tears" from the trial participants when they found out no further treatment was necessary, per the Times.
Standard treatment involves a grueling combination of surgery, multiple chemotherapy drugs, and radiation to destroy cancer cells, often with nasty, permanent side effects such as nerve problems, infertility, and bowel and sexual dysfunction.
Cercek said in a press release that the implications of standard cancer treatment on people's quality of life were "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 of dostarlimab's potential.
The cases of colorectal cancer among younger adults are projected to double by 2030, the MSKCC has said.
Dostarlimab works by helping the immune system identify and destroy cancer cells. The drug, which is branded as Jemperli, is already used for patients with endometrial cancer, but it wasn't clear if it would work for rectal malignancies. The participants in the trial had a type of rectal cancer called "mismatch repair deficiency". About 5 to 10% of people with rectal cancer have this type of cancer, where the genes responsible for correcting any mistakes during cell replication are faulty. The study can't tell us if dostarlimab will work in patients with other types of rectal cancer.
We don't know if it's a cure
Hanna K. Sanoff, an oncologist at the Lineberger Comprehensive Cancer Center at the University of North Carolina, wrote in a New England Journal editorial that it was a "compelling" study.
Sanoff cautioned that the outcome was an imperfect proxy for long-term cancer control. "Cancer regrowth occurs in 20 to 30% of such patients when the cancer is managed nonoperatively", she said.
Sanoff added that it was unclear if it would be safe to roll out the drug on a large scale because it required specific imaging techniques, such as PET scans, that aren't readily available, and could mean possible tumor regrowth is missed.
The study was also too small to show rarer side effects, Sanoff said.
Possible side effects of this drug include immune-mediate reactions in any organ such as inflammation of the lung. The most common side effects in patients that have taken the drug for endometriosis include fatigue, nausea, diarrhea, anemia, and constipation.
"These results are cause for great optimism, but such an approach cannot yet supplant our current curative treatment approach," Sanoff said.