As I understand it, having had Hodgkins when I was younger: Lymphoma will be called out specifically because lymphoma is potentially a relatively simple mutation. Cancer needs a bunch of unusual major characteristics from cells, and the lymphatic system already has all but one of those characteristics, it makes cells that are intended to wander about the body (whereas say your skin cells or brain cells are designed to always stay in one place), it sometimes makes lots of them (to fight disease, whereas most cells are replaced only slowly over a long period), however the cells aren't supposed to refuse to self-destruct. If a mutation disables the self-destruct in a lymphatic cell line now you've for a recipe for cancer.
So if it's just one or two mutations, on the one hand it becomes more likely that you get it (and we see lots of 20-something men get Hodgkins whereas obviously very few of them get stuff like lung cancer) and on the other hand it is easier to cure, basically just kill the patient slowly, cross fingers the cancer cells die first then you save the patient.
That's a very high level idea of the plan for the chemotherapy + radiotherapy used. In medicine the goal is to find reliable ways to do this that kill the fewest patients while reliably getting rid of the cancer, and then also aiming not to make the side effects suck too badly when you cure people (e.g. my lungs are trashed so that I permanently have a mild cough, which wasn't a huge annoyance for a middle aged guy who frankly doesn't eat well enough or exercise anyway, but I can see it'd ruin your life if you were previously a world class athlete and now you'll never achieve that potential). But obviously Mother Nature could very easily randomly cure some people from a single mutation by luck.
To add to your point, lymphoma is special because stage IV does not _inherently indicate mutagenic burden or tumor diversity.
Metastatic solid tumors _have to had "privilege escalation" mutations. AND those _indicate an overall greater genetic diversity.
As always diversity promotes adaptation and here evolutionary evasion of the disease.
However, staging incidentally still correlates with survival in non-hodgekins lymphoma as it's generally a nasty tissue class misbehaving. Treatment options got much, much better tho, with monoclonal antibodies and immune therapy.
So if it's just one or two mutations, on the one hand it becomes more likely that you get it (and we see lots of 20-something men get Hodgkins whereas obviously very few of them get stuff like lung cancer) and on the other hand it is easier to cure, basically just kill the patient slowly, cross fingers the cancer cells die first then you save the patient.
That's a very high level idea of the plan for the chemotherapy + radiotherapy used. In medicine the goal is to find reliable ways to do this that kill the fewest patients while reliably getting rid of the cancer, and then also aiming not to make the side effects suck too badly when you cure people (e.g. my lungs are trashed so that I permanently have a mild cough, which wasn't a huge annoyance for a middle aged guy who frankly doesn't eat well enough or exercise anyway, but I can see it'd ruin your life if you were previously a world class athlete and now you'll never achieve that potential). But obviously Mother Nature could very easily randomly cure some people from a single mutation by luck.