Well, that’s a great idea but Meth heads typically only need one methamphetamine product, the best one. Cancer patients have different needs and might need many different drugs. I’m not saying Walt couldn’t do it, and I know I’m nit-picking about a fictional character, but it would be considerably more difficult to use his abilities as a chemist (not a doctor or pharmacist) to successfully treat cancer patients. Otherwise, he probably would’ve opted to treat himself first.

I guess that’s the point of the series, he had to do evil to save himself and he lost everything worth living for.