Abstract: The present disclosure relates to detecting microsatellite indels in cancer patients and those at high risk for cancer, and is useful for early detection of specific types of cancer and early onset of relapse. More particularly, the present disclosure relates to compositions, methods, and kits for classifying and treating neoplasia and tumors with microsatellite instability. The instant classifier identifies preferred therapeutic options, including combination therapies, for MSI tumor or cancer, and is particularly useful for patient stratification so that patients who would be treatable by immunotherapy drugs may be identified at a very low cost.