GSK (LSE:GSK) on Monday announced that the US Food and Drug Administration has approved Jemperli (dostarlimab) as the first and only immunotherapy for adults with stage II and III MSI-H/dMMR locally advanced rectal cancer, cleared under the agency's accelerated approval pathway.
The approval targets a biomarker found in roughly 5% to 10% of rectal cancers, where tumours carry a genetic defect that leaves them unable to repair DNA damage, a trait that tends to make them highly responsive to immunotherapy.
Standard treatment for locally advanced rectal cancer has relied on chemotherapy, radiation and surgery, interventions that can carry lasting consequences including bowel, urinary and sexual dysfunction, secondary cancers and infertility. For patients with the MSI-H/dMMR biomarker, Jemperli monotherapy could allow them to avoid those treatments altogether.
"For decades, treatment has relied on chemotherapy, radiation and surgery," said Tony Wood, GSK's chief scientific officer, adding that the approval "represents an important step towards more personalised care for these patients."
The approval rests on data from the phase II AZUR-1 trial, in which investigator-assessed results showed 68% of evaluable patients achieved a sustained clinical complete response at 12 months.
In an exploratory analysis, 76% of evaluable patients showed no evidence of cancer a year or more after treatment, a group that includes those who reached complete response without surgery plus others confirmed through tissue analysis following surgery.
No disease recurrences have been reported among responders after a median follow-up of more than two years.
Data on the trial's primary endpoint, assessed by independent central review, continue to mature, with 47% of evaluable patients having achieved a 12-month clinical complete response and a further 38 participants still progressing toward that follow-up point.
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Serious adverse reactions occurred in 20% of patients receiving Jemperli, with fatigue, rash, diarrhoea and pruritus the most common side effects; 3% of patients discontinued treatment permanently due to adverse reactions.
Jemperli held FDA Fast Track and Breakthrough Therapy designations for this indication, and the application received Priority Review and a National Priority Voucher, pulling the approval ahead of its original decision date.
The application is under concurrent review by international health authorities through the FDA's Project Orbis initiative, with reviews ongoing in participating countries.
GSK said it plans to present full data from the AZUR-1 interim analysis at the European Society for Medical Oncology Congress this month.