 When people get heart or kidney transplants, they must be given immunosuppressive drugs to prevent rejection of the new organ. What do you suppose happens to cancer rates in those individuals who are immunosuppressed? Well, for some types of cancer, like skin cancer, the risk goes up, which supports the so-called immune surveillance hypothesis. The idea that our immune system acts as a natural defense system for keeping cancer under control. This could explain why as we age, and our immune function declines, our risk of cancer goes up. Here's a video of our immune system in action. That big oval cell in the middle is a cervical cancer cell, and those little round cells are our T cells delivering the poison pill, setting off the cancer cell self-destruct mechanism. And there it goes. Bye-bye cancer. That's the apoptosis, or program cell death, that I'm always talking about. Note this so-called renaissance of the immune surveillance hypothesis was more than 10 years ago. The problem with that theory is that for some cancers, immunosuppression decreases cancer risk. After a kidney transplant, your skin cancer risk may go up, but your breast cancer risk goes down. Your rectal cancer risk goes down. Why would people with depressed immune systems have less cancer? This led to a new theory, kind of the flip side of immune surveillance. The thought that in some sense cancer may be considered an autoimmune disease. See, the only reason the immune system is even able to pick out cancer cells from non-cancer cells is because tumors express foreign-looking antigens, immune-stimulating molecules. Why would tumors do that? Why would cancer cells go out of their way to wave a red flag around, saying, hey, come get me? We think it's because cancer tends to thrive in a setting of low-level inflammation. There's lots of examples of chronic inflammation leading to cancer, like ulcerative colitis to colon cancer, chronic pancreatitis to pancreatic cancer, chronic hepatitis turning into liver cancer, stomach inflammation to stomach cancer. Oftentimes inflammation, the body's immune response, can further cancer's agenda. By inciting an immune response, cancer creates its own inflammation, which may stimulate angiogenesis, help bring blood to the tumor, and help it grow. So the curve may look something like this. A low level of inflammation stimulates cancer growth, but if the immune system really catches on, then it can actually start hacking away at the tumor and slow it down. This may explain a mystery surrounding Kaposi sarcoma, a cancer affecting those with AIDS. When you start treating AIDS and the immune system starts to recover, you can actually see a flare in the cancer. So what are the dietary implications of this new autoimmune theory of cancer? Stay tuned.