“Tumours that are MSI high have a lot of mutations on their surface. A lot of mutations are needed for the immune system to recognise the cancer.
For the majority of solid tumours, the immune system doesn’t really care that you have cancer.
But in tumours that are MSI-High, they have a lot of proteins on their surface that are kind of like signs for the immune system to say ‘Hey, I’m here! Come fight me!’ And then the immune system sees those mutations, kicks in, and sends T cells.”
If the tumour is dMMR/MSI-H, additional tests are required to determine if the MSI-H is caused by Lynch syndrome….”
Lynch Syndrome Ireland 