Having a child changes a woman's life in the biggest ways possible. It also seems to have the potential to change the mother in a tiny but very important way. When a woman is pregnant, cells from the developing fetus often enter the mother's bloodstream, and some of them even set up long-term residence. A recent study from the Fred Hutchinson Cancer Center at the University of Washington suggests that these fetal cells may be more than just quiet passengers—they may also protect the mother from breast cancer.
For many years, it's been known that the risk of breast cancer is lower in women who have had children than in those who have not. There have been many theories about why this is the case, most of which focus on the word hormones and are accompanied by a lot of hand waving.
We also know that patients who receive bone marrow transplants from less compatible donors have a lower risk of developing new cancers. The leading theory for this observation is that the foreign bone marrow cells can more easily recognize and attack cancer cells in their new host's body. Putting these two sets of observations together, Vijayakrishna Gadi and Lee Nelson hypothesized that the persistence of fetal cells in the maternal circulation might protect mothers from breast cancer in a manner similar to the protection afforded by a bone marrow transplant.
To test their hypothesis, the investigators looked for the presence of fetal cells inthe blood of women with and without breast cancer. Now, finding these fetalcells is no small task. If half of your child's DNA is from you, after all, how can you be sure that the DNA you find in your own blood wasn't yours in the first place? The investigators found a clever way around this dilemma: They looked for DNA found on the male, or Y, chromosome. If a mother ha sY-chromosomal DNA in her blood, it's a good bet it came from cells that were originally part of a male fetus. Ideally, it would have been nice to identify cells from both male and female fetuses, but for testing a new hypothesis, this was a certainly a good way to start.
When the investigators looked at 35 women with and 47 women without breast cancer, they found some fascinating numbers. Forty-three percent of the women without breast cancer had male DNA, compared with only 14 percent of the women who had breast cancer. Those numbers translate into a 4.4-fold increased risk of breast cancer among women who didn't have male fetal DNA.
What does this mean in real life? Well, I still think a regular mammogram is a bette rlong-term strategy than having lots of kids and hoping that their DNA sticks around. And if fetal cells protect women from breast cancer, they might also safeguard against other tumors. We'll have to wait and see if that turns out to be the case. Finally, fetal cells are not always good guys; their presence has also been associated with the development of some autoimmune diseases. For me, the most exciting part of this story is how connections (and discoveries) get made when scientists think outside the box.