For metastatic colorectal cancer, is it possible for the tumor to be mismatch repair proficient at primary site but mismatch repair deficient at metastatic site?  

This is a very interesting question, and most of the time we think the MSI/MMR status between the primary site and the metastatic lesion is consistent. However, some studies suggest there could be some inconsistent results in colorectal cancer patient. In a small study with 40 metastatic colore...