Keytruda, pembrolizumab, (what he probably received) can only do so much. If it was in his GI tract it was also elsewhere in multiple places. The PD-L1 drugs at this point have more than 400k patients treated, with decent efficacy. I'm sorry for your loss. If his melanoma had metastasized to his GI tract it was too late for anything except palliative care.

This drug has been used in a huge number of patients for more than 11 years; the next gen of drugs is currently being used. I'm sorry for my curt style of writing, but - people like your father have helped pave the way for that next generation of drugs by constraining clinical trial designs.