Current estimates attribute 5% of cancer deaths to occupational factors and 2% to environmental pollution. In terms of the estimated lifetime risk of any cancer (currently 40% for men and 35% for women) this represents a substantial burden of disease.

In the fourth article in the CMAJ series on Environment and Health, Dr. Richard Clapp reviews the relationship between environmental exposure and cancer, its implications for cancer prevention and the physician�s role in screening for hazardous exposure.

Environment and health: 4. Cancer � R. Clapp