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Merck Drug Helps Colon Cancer Patients With DNA Repair Defect

A small study found that Merck & Co.’s immune system-triggering drug Keytruda shrank tumors in colon cancer patients with a specific gene flaw, showing that genetic tests may help identify those likely to benefit from immune therapy treatments.

The genetic defect, called mismatch repair deficiency, affects about 15 percent of colon cancer patients as well as a minority of patients with endometrial, bile duct and various other tumors. It leads to cancers with huge numbers of mutations because patients’ cells can’t fix “mismatches,” or genetic spelling errors, that sometimes occur as genetic material is synthesized in the body.