It's nearly impossible to link a single case of cancer to a particular cause, since the whole process is deeply probabilistic. Absent evidence of routine abuses at this factory and a significant increase in cancer incidence among workers, it doesn't really work.
A knee injury, on the other hand, is trivial to link to the on-the-job accident that caused it in many cases.
A knee injury, on the other hand, is trivial to link to the on-the-job accident that caused it in many cases.