Finding a cure for cancers originating in a particular organ is at least somewhat narrower than finding a "cure for cancer", and as such probably not quite as u

Finding a cure for cancers originating in a particular organ is at least somewhat narrower than finding a "cure for cancer", and as such probably not quite as unrealistic. You're still right, of course, since there are still (probably, haven't checked) multiple different kinds of breast cancer, and also because no cancer is curable if it has spread wide enough. Testicular cancer nowadays has cure rates of 90 to 95 percent or so (close to 100% for certain types, above 80% for others), thanks to chemotherapy that happens to be very effective against those kinds of tumours. So it's not an entirely unrealistic idea that you could find a cure that works in a large majority of cases if you limit yourself to something narrower than "cancer". Of course how easy or difficult or realistic it is to find that kind of a cure even for a more limited range of cancers still depends on the type of cancer and whatever other factors there are, because, well, it is a bunch of rather different disease.