An immunotherapy drug could spare bowel cancer patients the need for surgery and chemotherapy after results showed it was effective in 100% of cases.

Jemperli (also called dostarlimab) from GSK showed “unprecedented results”, the firm said, with no evidence of disease in all patients treated.

Everyone on the drug had locally advanced mismatch repair deficient (dMMR) rectal cancer, a form of bowel cancer, according to data presented at the American Society of Clinical Oncology (ASCO) conference in Chicago.

Jemperli is already approved on the NHS for women with some types of advanced or recurrent womb cancer.

The data showed all 42 patients in a trial led by Memorial Sloan Kettering Cancer Centre in the US had a complete response to treatment, with no evidence of tumours on scans.

The first 24 patients have been followed up so far for 26.3 months on average.

Studies suggest (dMMR) rectal cancer accounts for 5-10% of all rectal cancers.

Hesham Abdullah, a senior vice president at GSK, said: “The data showing no evidence of disease in 42 patients is remarkable.

“These results bring us one step closer to understanding the potential of dostarlimab in this curative-intent setting for patients with dMMR locally advanced rectal cancer.

“We look forward to evaluating dostarlimab in certain colorectal cancers in our ongoing AZUR-1 and AZUR-2 registrational studies.”

The current standard of care for patients with this type of cancer is chemotherapy plus radiation, followed by surgery.

Andrea Cercek, principal investigator for the phase II study, said the new treatment showed “durable complete tumour regression without the need for life-altering treatment” such as chemotherapy and surgery.

She added: “As a clinician, I’ve seen firsthand the debilitating impact of standard treatment of dMMR rectal cancer and am thrilled about thepotential of dostarlimab in these patients.”