Cure disease magics seem so effective that medicine is little beyond that. In Morrowind there were some quest that only involved fetching potions to sick people in isolated places. And "something like cancer" really sounds as "something like corprus" in TES. I even remember a concept art of a corprus beast that was basically a tumor with two legs!
Cancer isn't known to make you immune to age or give you abnormal strength, though, but it does kill you, which corprus can do.
As to the exact limits of what one can do with restoration magic, it's hard to say, since in general, while certainly, in game, of course, what magic can do has its limits. But in lore, the limits of magic don't seem to be clearly defined, if there are any at all beyond what the caster's skill, knowledge and imagination allows, and if there is any logic to the matter, since people are still researching magic, one could assume that over time, people's knowledge of magic may expand, and they may find ways to do things once thought impossible, so even whatever current "limits" there may be on magic may not actually be hard limits on the actual capabilities of magic, but rather, the limits of the caster. Just as how there are things which modern technology can't do that aren't physically impossible, just beyond what the technology we have can achieve.
Now that we've good that out of the way, we should look at what we
know restoration can do first. The most obvious things are what it can do in the games. We've had spells to heal wounds, restore attributes, heal diseases, even fortify attributes, and some other effects. But what, exactly, is it capable of in lore? Can restore health spells reattach severed limbs? This I don't know. It's true that it can restore a character who is near death to perfectly good health in the game, but no matter what kind of injuries the player recieves, you can't actually lose any limbs, so unless there are instances in lore of it being used to heal dismemberment, I'd say we really can't be sure if it can do that or not. As to cure disease, in the games, it can cure any disease instantly, aside from blight disease in Morrowind (That needs a different spell.) and some special conditions like vampirism and lycanthropy. But in those two cases, it might be because once you get to the point where you can't be cured by a simple potion, the condition goes beyond a simple disease, after all, one condition makes you become a blood svcking monster with special powers and weakness to sunlight, the other makes you transform into a beast under the right condition, I'd say that at that point, it has already changed you into something different from what you were before, so naturally, normal cures still work on it. The fact that several quests involve the use of normal cure disease potions or spells to cure diseases suggest that a generic "cure disease" effect may really be as versatile in lore as it is in the game, though, as at that point, it's already become a plot point, and the general rule of designing games is that if you don't want an aspect of gameplay to also be considered to reflect how thungs are in the story, you should not have characters acknowledge it. Still, I would imagine there's probably some other special diseases that can't be cured using normal cure disease potions.