Cancer is the no. 2 cause of death in the US, second only to heart disease. Some cases of cancer are out of our control, determined by genetic defects and predispositions passed down from one generation to the next, or spurred by genetic changes we undergo through our lifetime. But we also know that breathing in certain substances, eating specific things, and even using some kinds of plastics ups the risk of developing some deadly cancers. Here are some known cancer-causers linked to cancer.