It is ultimately up to you, and some what the state laws, if they say ALL pets have to be vac against rabies, indoors or not.
I personally vacinate all my animals indoors or outdoors.
About the cancer, this is true, some shots can cause this, but it doesn't happen 100% of the time, it actually happens less then it does appear.
Now adays people are trying to give their cats shots in their legs, as low as possible, so if it does develope into cancer it is easier to remove and they have a higher success rate. And if it DOES worsen, there is the option to remove the leg, vrs if you get the shots between the sholder blades, it's harder to remove those, and you can't really amputate the sholder area!
This is how I think of it...
What if some day, one of my animals bit... and they were not vacinated, they could be put to sleep because I had no proof that they were not rabid.
Also, what if by chance a wild animal gets into your house some how ( or your animal escapse outside.) And it encounters an animal that DOES have desease's, your pet is then unprotected, and can die, and also spread it to the other animals, or to you.
I don't have any bookmarked links on more indepth info, though I can get some if you like. However I'm sure someone else here has info for you and they'll get around to posting it.