Wednesday, August 8, 2012
Why cancer often comes back and usually can’t be cured by chemotherapy
Many years ago I saw a woman who had had breast cancer treated with surgery about 20 years earlier. She was sent to me because she had developed an enlarged lymph node that contained breast cancer. To everyone’s surprise the cancer had returned. What took so long? Cancer is supposed to grow. Surely it wasn’t growing for 20 years. It would have made its presence known well before then if it were. Now we know the answer to this riddle – Stem Cells. Stem cells are cancer cells that don’t grow. They exist only to provide the growing cells that kill people. It turns out at least in animal studies, that after a cancer develops, some of the cells go into a kind of hibernation, while the others continue to grow and spread. So when we treat patients with chemotherapy and apparently rid the body of all the cancer cells we can detect, we haven’t really completed the job. The stem cells are still there and some of them may begin to divide and form new tumors throughout the body – maybe even 20 years later though generally we see the cancers come back much sooner. Why aren’t these stem cells killed by the chemotherapy? Chemotherapy mainly kills dividing cells and these hibernating stem cells are not going to be affected by the drugs. How about all the new targeting drugs? Well they are designed to slow the growth and division of cancer cells so stem cells aren’t going to be knocked out by these. These new studies explain a lot of what happens in cancer treatment. First there is surgery often followed by what we call adjuvant therapy. This can be radiation or drugs, sometimes chemotherapy, sometimes hormones such as in the case of breast or prostate cancer. Now doctors are using the new targeting drugs that strike growth-promoting molecules in the cancer cell. And then we wait and see. Many times, nothing happens. A cure. Sometimes though, in a while – perhaps a very long while the cancer comes back and more treatment is needed – but not likely to be curative. The stem cells haven’t been eliminated and are beginning to activate. Why? No one knows - yet. So there is good news and bad news. We know why the cancer comes back – good news. But, we haven’t a clue – yet – how to kill these stem cells.