[chrisamiller]

There is a lot of great work going on thinking about this very problem. One common theory goes like this:

There are lots of tumor "driver mutations" that are causative and occur in lots and lots of patients. These would make great targets for a vaccine like this, in theory.

But - Tumors have to evade the immune system in order to gain a foothold. (We have all had many cancerous cells that were cleared away without anyone ever knowing!). If a mutation is particularly good at activating the immune system, it's unlikely to survive long enough to cause cancer. So one of the features that a mutation has to have in order to become a driver is that it's bad at being recognized by the immune system! That means the most common mutations that we'd like to target with cheap, mass-produced vaccines may not work very well.

There's some evidence on both sides at this point, with lots more data being collected, but it's certainly something that us folks researching the problem are keenly following!