Cancer and the Immune System

My understanding of cancer has changed radically over the past few months. I used to think of it as an inevitable consequence of aging, a stochastic certainty. The human body is made of about 50 trillion cells, many of which replicate their DNA and divide regularly. It's only a matter of time until one of those cells randomly accumulates the wrong set of mutations, and loses the molecular brakes that restrict uncontrolled growth.

Strictly speaking, the idea is correct. That is how cancer begins. However, there's another check in place that operates outside the cancer cell itself: the immune system. A properly functioning immune system can recognize and destroy cancerous cells before they become dangerous to the organism. In fact, your immune system has probably already controlled or destroyed a number of them in your lifetime.

I recently read a fascinating account of some preliminary findings from the lab of Dr. Zheng Cui at Wake Forest university. His group took blood samples from 100 people and purified a type of immune cell called the granulocyte. They then evaluated the granulocytes' ability to kill cervical cancer cells in a cell culture dish. They found that it varied dramatically from one individual to another. One person's granulocytes killed 97% of the cancer cells in 24 hours, while another person's killed 2%.

They found some important trends. Granulocytes from people over 50 years old had a reduced ability to kill cancer cells, as did granulocytes from people with cancer. This raises the possibility that cancer is not simply the result of getting too old, but a very specific weakening of the immune system.

The most important finding, however, was that the granulocytes' kung-fu grip declined dramatically during the winter months. Here's Dr. Cui:

Nobody seems to have any cancer-killing ability during the
winter months from November to April.

Hmm, I wonder why that could be?? Vitamin D anyone??