The extremely lethal and highly contagious Ebola virus strikes fear, appropriately, in most of us. The human immunodeficiecy virus (HIV) is another scary virus, but we’ve become pretty blasé about that one. Fear is an interesting thing.
Cancer also invokes fear. When someone finds out that I’m doing cancer research in the basement of MY HOME, I get to observe a range of interesting facial expressions. But is cancer contagious?
For the most part, the answer is “no,” in the same way that a mouse kidney would not survive if it were transplanted into human me. That’s because I have an immune system that can distinguish between foreign and self. I can even inject mouse cancer into myself, and my immune system would immediately destroy it, not because it is cancer, but because it sees MOUSE cells. But the immune system doesn’t just tell the difference between human and mouse (a monkey can do that). It also can differentiate between fraternal twins. That’s why medications that shut down the immune system are critical for an organ to be transplanted from one person into another, UNLESS the organ donor and recepient are identical twins.
So here is a brief history of how cancer research became possible in animals. In order to carry out experiments to study diseases and develop new treatments, variability needed to be minimized. You can’t have random types of wild mice in an experimental group, where a treatment works “sometimes,” depending on the type of mouse. Plus you can never repeat the exact experiment, because you would have to use different types of mice each time. Then scientists figured out that by inbreeding and inbreeding over and over again, you end up with mice that are essentially “identical twins.” C57BL/6 is a black mouse, and the most common strain used in medical research. Now one day, in 1951, Dr. Margarent Reed Lewis had a bunch of C57BL/6 mice, and in one of them, a lung cancer spontaneously developed. She took that cancer and surgically implanted it into another C57BL/6 mouse, and it grew! Eventually when the tumor got big enough, a small piece was transplanted into another C57BL/6 mouse, and it grew. This cancer, now called Lewis lung carcinoma, has been growing in mice for the last 68 years!! Yes, one of the characteristics of cancer cells is “immortality.” But if I inject this cancer into another mouse strain, it won’t grow. If I inject it into myself, it won’t grow. So I can take off the red hazmat suit.