IHC or MSI testing is also done on some other tumors to evaluate the likelihood of Lynch or to determine whether to use immunotherapy drugs, Weiss said.

About 16% of people with colon cancers diagnosed before age 50 have tumors caused by inherited genetic mutations, and BRCA and other genes are involved in some breast, ovarian and other cancers. That had led some researchers to push for genetic testing of patients without the intermediate step of IHC or MSI testing, Weiss said.