<qa>  What is the most effective treatment against?Mismatch repair genes normally serve to fix the small glitches that occur when DNA is copied as cells divide. In 1993, researchers discovered that mutations in human mismatch repair genes play a key role in the development of certain forms of colorectal cancer; individuals who are deficient in these mismatch repair genes are at high risk for colorectal cancer. Accumulating evidence has shown that immunotherapy may be most effective against these cancers. 