What causes human cancer?

1. Lung cancer is the leading cause of cancer death in American men and has now surpassed breast cancer as the leading cause of cancer death among American women. 2. Heavy alcohol consumption is associated with increased cancer risks. 3. Intercourse at an early age and multiple sexual partners have been linked to an increased risk of cervical cancer. 4. The most widespread environmental carcinogen, accounting for the majority of superficial skin cancers and some types of melanoma, is ultraviolet radiation from the sun.