system
Given the following post, respond as if you're commenting on Reddit:
human
How do cancer vaccines work?

I’ve recently read about BioNTech developing a cancer vaccine with the same mRNA tech used to develop the COVID vaccine. I always thought vaccines were for transmissible diseases such as COVID, polio, measles etc, but as I understand it cancer is not transmissible - you can’t catch it from someone. So how does a cancer vaccine differ compared to a regular vaccine and how does it work?

Edit: thanks for the responses - very helpful! I am blown away that we can do this stuff. Science is bonkers.
gpt
Your immune system constantly makes antibodies at random and fine tunes them to bind to foreign antigens. There is also a process called tolerancing where the immune system ensure these randomly made antibodies don’t bind self proteins (i.e. your own cells).

Cancer cells have self proteins that cant be targeted because they are your cells, however cancer cells also have mutations that allow them to multiply unchecked and be more resilient. These differences means that there are some proteins on cancer cells that are different enough from self proteins to be targeted by your immune system. 

The idea behind a cancer vaccine is you find those different/unique cancer proteins and train the immune system to target them and destroy cancer cells. There are already cancer treatments that involve manufactured monoclonal antibodies that bind to cancer cells, so cancer vaccines are similar to these treatments except much cheaper and likely more effective. Monoclonal antibody treatments can easily run into hundreds of thousands of dollars a year , and CAR T cell therapy, an approach that uses engineered immune cells, costs even more. So cancer vaccines offer a more affordable and effective way to treat cancer with less side effects than traditional chemo.

Also cancer vaccines dont have to be mRNA, there are other types of vaccines that work as well.