The immunotherapy drug dostarlimab has demonstrated a 100% efficacy rate during the phase II clinical trial among a dozen patients with mismatch repair-deficient locally advanced rectal cancer.
Dostarlimab is an anti-PD-1 (Programmed cell death protein 1) monoclonal antibody, an inhibitory receptor present in some tumor cells, and reduces active T-cells that cause the deregulation of the immune system. Researchers said that a longer follow-up is needed to determine how long is the immunotherapy drug effective in the patients who participated in the study.
Rectal Cancer Subset Vs. Dostarlimab
Dr. Andrea Cercek, a medical oncologist and section head of colorectal cancer at Memorial Sloan Kettering Cancer Center told Healio that patients with mismatch repair-deficient, locally advanced rectal cancer, are typically treated with chemotherapy, radiation, and surgery.
However, some patients are resistant to chemotherapy while radiation and surgery could cause short- and long-term bowel, bladder, and sexual dysfunction.
Dr. Cercek noted that this subtype of rectal cancer is sensitive to checkpoint inhibitors. So they hypothesize that PD-1 blockade with dostarlimab will be effective as chemotherapy replacement and potentially eliminate the need for radiation and surgery in cancer patients with that rectal cancer subtype.
The team of researchers sought to assess how the subset would react to the checkpoint blockade and whether patients who received it could skip chemoradiotherapy and surgery.
The study, titled "Improving Treatment Approaches for Rectal Cancer" published in the New England Journal of Medicine, involved 14 patients with a median age of 54 and with mismatch repair-deficient stage II and stage III rectal adenocarcinoma. They were given dostarlimab every three weeks for six months, followed by standard chemotherapy, radiation, and surgery. The median follow-up was about 6.8 months.
Promising Results from the Study
The team found that the 14 patients with at least six months of follow-up showed a 100% positive response to dostarlimab. They found no evidence of tumor in the biopsy, digital rectal exam, endoscopic visualization, fluorodeoxyglucose-PET, or MRI.
More so, none of the participants experienced disease progression or recurrence, and none of them required to undergo further chemotherapy, radiation, and surgery. Researchers also recorded no serious grade 3 or higher adverse effects.
UNC Lineberger Comprehensive Cancer Center's Professor Hanna K. Sanoff, one of the study authors, told Science Daily that the initial findings of phase II clinical trial are remarkable and will benefit future studies in using dostarlimab against the rectal cancer subtype.
On the other hand, Professor Sanoff said the findings should be viewed with caution since the participants were only observed for six months to two years so far. Therefore, further study is needed to confirm the results.
She noted that there are other immunotherapy drugs that could be tested against this form of rectal cancer that will also offer the benefit of avoiding surgery, chemotherapy, and radiation.
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