I came here wondering, "what? a "vaccine" for cancer?" and read the article. Am I right to interpret it as: "we gather cancer cells from a specific patient, assemble a unique identifier for those cells we don't want, and then teach the immune system to identify and attack those cells"?

I guess that indeed that is a vaccine. I always interpreted "vaccine" as "teaching your body how to kill foreign organisms by training it on what the organisms "look" like." (yes, this abstraction is certain to be way oversimplified)

Great to keep in mind that this has not been peer reviewed but I’d rather be optimistic than pessimistic about this. Wouldn’t it be nice if the pandemic in some roundabout way speeds us towards better cancer treatments.