I don’t ordinarily spend a lot of time thinking about how quickly the cells in my body grow. But one of the many benefits of cancer Is that it’s giving me an insight into that question. I’m now learning a bit about this and particularly about how it affects every aspect of the cancer and chemo treatment.
Many cancers are detected in the first place because the cancer cells grow so much faster than the surrounding cells. For example, a skin cancer might show up as a spot or lesion on the skin that enlarges much faster. Other cancers show up as launch center of the skin or processes that interfere with normal body function.
In my case (ALCL) I did not detect cancer in this way. The cancer cells were in fact growing much more quickly than ordinary cells but that was all happening internally, in the abdominal lymph nodes.
A key part of my cancer diagnosis was a PET scan. This is an imaging test done using hybrid PET/CT cameras. It uses 18F-sodium fluoride as a marker. This radioactive substance lights up the most quickly growing cells. In my case this showed brightly lit abdominal lymph nodes. There was also some involvement of bone marrow and spleen, indicating possible cancer cells growing quickly, but not as quickly as in the lymph nodes.
The actual chemo treatment also depends on differential cell growth rates. The cytotoxins kill the most actively growing cells (the cancer), but fewer of the regular body cells. The theory is that one can keep zapping the cancer without doing irreparable harm to the rest of the body.
The most obvious effect of differential cell growth rates is in the side effects of the chemo therapy. For example, I lost the dark hair on my head but not the white hairs. This is good in the sense that I’m not completely bald, but it also shows that the cells that generate the dark hairs on my head are more alive (growing faster) than the cells that generate the white hairs.
I’ve also lost some of the hair under my arms but very little of the hair growing on the tops of my arms. One of the worst effects is in my mouth. The cells in the lips, gums, tongue, and interior of the mouth are rapidly growing cells that are affected more severely by the chemotherapy than are other cells in the body.
A good, accessible resource on cell growth is Cell Biology by the Numbers by Ron Milo and Rob Phillips. Their chart makes clear why chemo affects the digestive system, blood cells, and mouth cells more than say, fat or skeletal cells.
They point out that hair grows at about 1 cm per month, while fingernails grow at about 0.3 cm per month. Coincidentally, that is about the same speed as the continental spreading in plate tectonics that increases the distance between North America and Europe.
That last factoid should come in handy someday; I’m just not sure when.