"Cancer" is a term for diseases in which abnormal cells divide without control. The term cancer is used to encompass a range of different diseases (eg adenocarcinoma of lung, melanoma, hepatocellular carcinoma). There are a number of well-known sets of circumstances which have demonstrated without doubt the link between some occupational exposures and some types of cancer. The problem arises when we examine more subtle effects on common cancers. The question then arises: "Is this cancer one which would have occurred anyway, or is it is a direct result of the person’s occupation?"