By the way, this indicates why it would be really good if you could detect cancers at 10 to the 4th cells and 10 to the 6th cells. And people are working on ways that they might be able to do that.
Now, these cancer, when I say they derive from a single cell, I also want to say that they arise because of mutations in the genome of a single cell. So the cancers usually arise from mutations in the genome. When you think about it, in your body from the time that you were a fertilized egg to now, you've had a total of about, well, during your lifetime, about 10 to the 16th cell divisions, give or take. That's what you've got; in your life, there's probably 10 to the 16th cell divisions, and the chance of a mutation arising in any particular gene per cell division is about 10 to the minus 6th: this is the chance of a mutation in a given gene. That varies between genes and all that, but that's a good guess. So if you had 10 to the 16th divisions and 1 in 10 to the 6th chance of mutation in a given gene per division, every gene has had mutations in it. Every gene has had mutations in it, despite the impressive fidelity of DNA replication that we talked about earlier in the course, that only one error per 10 to the 9th bases. A gene is 10 to the 3rd bases long. So that's about 1 in 10 to the 6th, and you've got 10 to the 16th divisions. That's a lot. Now, these mutations, most of them are happening during development. Some of them could happen before birth. You could have inherited some critical mutations as well. But the mutations can happen by chance, or you can accelerate your rate of mutations. (...)
Cancers usually start by random mutations in a single cell. Some mutations create a protein that fails to function properly increasing the likelihood for additional mutations. For example, if a protein in the mismatch repair pathway did not function properly, then more mutations would occur during replication. Cancers develop as a result of a variety of mutations. Although mutant forms of some proteins are found more commonly in cancers. Some mutations that occur in one cell can increase the likelihood of additional mutations occurring in the same cell." Eric Lander PhD. "Intro to Biology. The Secret of Life" MITx 7.00 MOOC.