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Immunotherapy on its own helped only a few patients with advanced small bowel adenocarcinoma, mainly those whose tumours had mismatch repair deficiency, so the drug is reserved for that group.
Multicentre single-arm phase 2 study of 40 patients with previously treated advanced small bowel adenocarcinoma given pembrolizumab every three weeks.
The objective response rate was 8 percent and the study did not meet its primary endpoint; responses clustered in patients with mismatch repair deficient or microsatellite instability high tumours, while microsatellite stable disease rarely responded.
Every small bowel adenocarcinoma should be tested for mismatch repair deficiency, because immunotherapy is worthwhile for those patients and of little use to the rest.