"Evidence from experimental studies does suggest that psychological stress can affect a tumor’s ability to grow and spread. For example, some studies have shown that when mice bearing human tumors were kept confined or isolated from other mice—conditions that increase stress—their tumors were more likely to grow and spread (metastasize). "

"Although stress can cause a number of physical health problems, the evidence that it can cause cancer is weak."

But they do make some statements that seem to support the idea as well.

Also, given that stress significant suppresses the immune system, and that the immune system is important for protecting against cancer growth, I think it is highly unlikely that stress wouldn't affect cancer.

https://en.wikipedia.org/wiki/Cancer_immunology