Heterogeneity of mismatch repair defect in colorectal cancer and its implications in clinical practice

- Microsatellite instability is considered as an early event in carcinogenesis of colorectal deficient DNA mismatch repair system without tumoural heterogeneity
- Here we have described a case of microsatellite instability presenting intra- and inter-tumoural heterogeneity
- Some precautions must be taken in microsatellite instability testing and immunochemistry of DNA mismatch repair proteins, especially before treatment with immune checkpoint inhibitors