If the cancer is always required to make a "move", and cannot make the same "move" twice, then it is possible that all available moves will make the cancer's position worse/lower it's score. This becomes increasingly likely as the number of possible moves decreases, and so is especially acute when the number of nodes that can be mutated is close to the height of the tree being searched. Therefore it should be possible for the cancer to make a null/neutral move in which no new mutation is selected, for completeness.
This might also affect treatment moves, so it would probably be easiest just to make it to make it available to the treatment player as well, although in practice as treatments do not stack it is unlikely all possible treatments will make things worse for the treatment player.
If the cancer is always required to make a "move", and cannot make the same "move" twice, then it is possible that all available moves will make the cancer's position worse/lower it's score. This becomes increasingly likely as the number of possible moves decreases, and so is especially acute when the number of nodes that can be mutated is close to the height of the tree being searched. Therefore it should be possible for the cancer to make a null/neutral move in which no new mutation is selected, for completeness.
This might also affect treatment moves, so it would probably be easiest just to make it to make it available to the treatment player as well, although in practice as treatments do not stack it is unlikely all possible treatments will make things worse for the treatment player.