A lot of things can cause cancer. For example, prostatitis and inflammation likely cause cancer, and likely are also correlated with it metastasizing. (I'm not claiming it's the cause or a sole reason but the evidence suggests it increases the risks.) I've never looked into parasites but it's possible parasites are associated with an increased relative risk of cancer, and the mechanism of action would probably be inflammation.

My guess is people are in effect checked for parasites by way of annual bloodwork and annual checkups. If someone started losing weight, for example, they'd go see a doctor who might investigate for parasites if the symptoms point to it. There is probably not much reason to do an annual parasite-specific test in people. Livestock cannot talk to us about their symptoms, and eat all sorts of crap, so there's some important difference there.