We don't know that "this drug makes the cancer completely visible to the immune system". It could easily be that, say, 0.1% of the cancer cells don't become vis

We don't know that "this drug makes the cancer completely visible to the immune system". It could easily be that, say, 0.1% of the cancer cells don't become visible for some weird reason, or they accidentally develop a protection against the immune response. It would look like complete elimination of the cancer on scans and in blood markers, but could come back in a few years. Only way to know for sure is to wait.