Halloween is nearly upon us, so I thought I’d tell you a scary (but true) story. It’s creepier if you read it with a Transylvanian accent (starting now).

Gather around, my dear ones, to hear the true story of vicious monsters and inept factory workers that live closer than you think.

Deep in the dark interior of all of your cells, every hour of the day and night, billions of tiny factories replicate your precious and life-giving DNA. This is a job of extreme importance: if even one factory worker makes one slip, a horrific mutation may arise – and from that wicked mistake an evil cancer cell may emerge.

If you think about the number of cell divisions we have in every 24-hour period (it turns out this number is 100 billion), there is a pretty good chance that someone in one of those factories will make a mistake (it turns out that the rate of accidents – the spontaneous mutation rate – is about .000001%).

Now, dear readers, comes the scary part. If you use the frightening numbers listed above, and perform the necessary calculations, you will find that the number of spontaneous mutations that arise every day in your own flesh and blood (not mine, because I am a vampire) is…100,000! Bwahahahahaha!!!

Okay, enough of the Transylvanian accent. I am freaked out enough just writing this.

Granted, some of these mutations would produce no clinical effects. But if even one of these mutations was in p53, RAS, RB, or any of the other genes commonly mutated in cancers, that could be the kiss of death.

There are two things that make me feel better after thinking about this chilling but true story:

1. We have awesome mechanisms for finding and fixing bad DNA. And if these fail, the cell will be instructed to kill itself.
2. If a cell with a mutation should make it through all these safeguards, our immune system has ways of killing that cell before it can cause a serious problem.

Here are some of the ways our immune system kills tumor cells:

1. The first line of defense is probably the natural killer cell, which is a big bad brute of a lymphocyte that can destroy tumor cells without prior sensitization. It doesn’t need to be told what to do: it just sees a tumor cell (or even a cell that might become a tumor cell) and bashes it to death.
2. Cytotoxic T cells also kill tumor cells, especially those that are associated with viruses (like EBV and HPV).
3. Macrophages collaborate with NK cells and cytotoxic T cells in the fight against tumors; they exert their effects by releasing reactive oxygen metabolites or secreting tumor necrosis factor (TNF).

That’s all for our scary story – unless you want to read more (in which case you should check out Robbins 10th edition, page 314). Happy halloween, everyone!