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.

3 comments:

Anonymous said...

How frustrating. My mother passed away from a relatively rare form of cancer, gallbladder cancer. Looking back now I wish we hadn't pushed her into chemo and radiation. It made her so sick and did nothing to extend her life.

It left me motherless. I hate cancer.

nando@lip cancer said...

although cancer is still hard to be eliminated, alternative treatment may prevent its growing. Like in my country, chinese traditional treatment is popular to cure cancer, eventhough it can't be proven the truth medically. I think belief is a matter in this case.

Greg Pawelski said...

Cancer stem cells (CSCs) are a hot topic in the scientific community. This subpopulation of malignant cells may one day provide an important avenue for controlling cancer, especially if new treatments that target the cancer stem cell are developed and combined with traditional chemotherapy and/or radiation.

Cancer stem cell biologists hypothesize that any treatment that targets the source of origin rather than simply killing all cells, healthy and malignant, would be an improvement over most conventional therapies.

Stem cells have that infinite ability to renew themselves and produce the many different cell types that make up a human. Cancer's hallmark is its ability to grow infinitely, multiplying into various cells that make up a tumor. Is cancer the result of a normal stem cell turned bad or an ordinary cell that somehow acquires astem cell's immortality and versatility?

In stem cell research, anti-cancer treatments often effectively shrink the size of tumors, but some might have the opposite effect, actually expanding the small population of cancer stem cells that then are capable of metastasizing.

This subpopulation of malignant cells (CSCs) may one day provide an important avenue for controlling cancer, especially if new treatments that target the cancer stem cell are developed and combined with traditional chemotherapy and/or radiation.