It's a metaphor. I personally think that "cancer" describes something that is deadly, awful, and spreads. Instead of saying those three things, or maybe more, it conveys the message to me more quickly.
It's a really poor metaphor, though. ICOs are stupid, but really easy to avoid (just don't put money into them). Certainly not "awful" in the way losing a loved one to an early, excruciating death is. They're not deadly and they don't "spread", at least not by any means remotely comparable to how cancer spreads.
It's not like the author works with the metaphor, either. The word appears exactly one time on the page, in the title. It's pure clickbaiting.
The cancer analogy is relation to the financial markets as a whole. Once people make more and more money from ICOs, they reinvest and push aside other more legitimate/productive forms of making money until there's nothing but ICO activity - investors who didn't jump on get FOMO and add to the new tide.
Despite some other rude commenters I agree with you. Cancer is a devastating, tragic disease and it's used flippantly often. I just tell myself that since those people are fortunate to be shielded from such a loss, that they are simply ignorant of the pain it brings people.
It's not like the author works with the metaphor, either. The word appears exactly one time on the page, in the title. It's pure clickbaiting.