Those spots on your teeth are probably super calcified spots. When those teeth were developing it may have been possible that you bumped your mouth, or that you ran a high fever and that is what causes your spots. You can try to either bleach your teeth with some over the counter bleaching trays like crest white strips in hopes that the teeth become similar in color to the white spots on your teeth. Or you could go to your dentist and have them try to fix the problem with calcium paste. Good luck, and don't worry you are by far not the only person that has that problem. :)
You might have cancer in your mouth only if you did chew tobacco or any tobacco products that have do with your mouth and if did you better go to the hospital right away they can solve it or treat it better go to doctor right away better safe than sorry good luck.
I had that, as soon as I saw it I brushed my teeth for a long time and used listerine 6 benifits it burns but that means it's working try that is it doesn't go away get your teeth cleaned at the dentist, it thy doesn't work then your stuck with them