Can you eat cancer cells without risk?
HeLa cells (which are of course derived from a cervical cancer) have actually been injected into humans to see if they would grow; they grew briefly but were promptly rejected. Similarly, surgeons have on occasion accidentally stabbed themselves and inoculated themselves with the human tumors they were operating on. 

Injecting human cancer cells is a far greater risk than eating non-human cancers, and even in that case the risks seem to be very low. 

There have been rare cases of people with profoundly suppressed immune systems (organ transplant recipients) allowing a transferred tumor to grow, so (though of course the risk there is vastly higher than merely eating a cell) it's not completely impossible. 

Pragmatically, it's very likely that everyone who's eaten, say, chicken has unknowingly consumed some chicken tumors.