Smoking constricts arteries throughout the entire body including the brain, which causes minor strokes due to the clotting blood and lack of circulation in small arteries. There are two major differences between sharks and every other animal on earth. The sharks skeleton is composed entirely of cartilage, and sharks never contract cancer. It seems that their completely cartilaginous skeleton is the reason behind their ability to remain cancer free. Bone contains blood vessels, cartilage does not.
Cartilage produces AAF, an anti-angiogenesis factor which inhibits blood vessel development.
In order for cancer to grow it depends on a lot of blood vessels to constantly supply a large blood flow. In government-supported research at MIT it was discovered that cancerous tissue growth secede when blood vessel production was interfered with by the shark cartilage. Tumor tissue was transplanted into the anterior chamber of rabbits eyes so it could be easily viewed through the transparent cornea. Blood vessel and tumor growth both stopped in the rabbits treated with shark cartilage. MIT also found that shark cartilage contained 1,000 times more AAF than that of the cartilage of any other animal.