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Marisa Weiss, M.D. Headshot

Breast Cancer's Evolution

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Marisa Weiss, M.D. Headshot

Breast Cancer's Evolution

Posted: Updated:

Click here to read an original op-ed from the TED speaker who inspired this post and watch the TEDTalk below.

As a breast cancer doctor who has been practicing for some 25 years, I have often wondered why the breast is the favorite place for cancer to occur in a woman's body. About 29 percent of all cancers in women start in the breast, more than any other type of cancer. Only 10 percent of breast cancers are due to specific inherited high risk genes, while 90 percent are mostly triggered by environmental and lifestyle factors.

So, what makes this organ so disproportionately affected by cancer? What role has evolution played in this modern-day public health crisis? And, how can evolution help us solve this huge problem?

There are a number of biological reasons why the breast is more vulnerable to cancer than any other organ. The development of the breast gland takes many years longer than other organs. Making an organ is a very delicate process. Each time the body creates a new batch of DNA to pass along to a nascent crop of baby cells, mutations can be introduced if the sensitive operation is insulted or disrupted in a significant way. For example, exposing an adolescent girl to radiation at the critical time she's building her breast tissue can lead to permanent gene mutations that increase her risk for breast cancer later in life.

Another biological reality is that once the breast gland is formed, it is an immature and highly proliferative (active) organ, unable to perform its job of making milk until it goes through the comprehensive maturation process of a full-term pregnancy and breast-feeding. Organs that have a job to do starting from birth like the brain, heart and kidneys, have a much lower risk of cancer. But an organ like the breast, which is immature and in waiting mode until the long maturation process is over and it can finally be put to work, is more likely to get into trouble.

So what was intended as an evolutionary advantage has turned into a curse of modern life, contributing to a significantly higher incidence of breast cancer.

In addition to these biological factors that have made breasts more susceptible to cancer, evolution may also have a hand in it as well. Evolution has been tinkering with the breast all the way down to the cellular level. And for good reason; after all, the survival of the species depends on feeding its young, making the breast critical to the perpetuation of the human race. The special evolutionary feature of breast cells involves estrogen receptors which are places in the cell that receive messages from the estrogen hormone that usually signal it's time to start to grow. Breast cells also have other receptors for different hormones, such as insulin growth factors, which are designed very specifically to only respond to that one type of hormone. In general, there is a very monogamous relationship between the receptor and its hormone (also known as a ligand). The one exception is the estrogen receptor which has the capacity to interact with many substances that can look like, smell like or taste like estrogen -- rather than responding only to estrogen itself. While providing this flexibility may have had the evolutionary purpose of ensuring milk could be produced under harsh circumstances that challenged the survival of the race, it also makes the breast more vulnerable to breast cancer in our modern-day world.

Leakey's father said that humans are the "only animal species that makes conscious choices that are bad for our survival as a species." Today, there are many more chemicals in greater volume in the environment that are hormonally active and therefore interact with breast cells in detrimental ways. They range from bisphenol A (in plastics, food can liners, and cashier receipts), phthalates (in personal care products like fragrances and deodorants, as well as in preservatives), flame retardants (in mattresses, kids' pajamas, upholstery, etc.), hormones in food (given to beef and dairy cattle to increase production), to pharmaceutical hormones in birth control pills and hormone replacement therapy after menopause. These chemicals are very new to our environment and to our bodies in evolutionary terms. One hundred years ago, they didn't exist and breast cancer was a relatively uncommon disease.

So what was intended as an evolutionary advantage has turned into a curse of modern life, contributing to a significantly higher incidence of breast cancer. While our bodies have not yet evolved to counter these assaults, our thinking must. We need to do a much better job of recognizing this evolutionary vulnerability and protecting girls and women from its effects. Louise Leakey says in her TEDTalk (February 2008), that evolution has also given us the collective intelligence to perform extraordinary advances to help people all over the world. As part of that effort, Breastcancer.org has embarked on an education program we call Think Pink, Live Green that provides practical and effective steps to help lower the risk of breast cancer based on evidence that currently exists. But we need to have a much greater understanding of the interplay between environmental and lifestyle factors and our breast cells to ultimately find the real answers to preventing breast cancer. It's time to stop thinking that breast cancer is unavoidable and invest in research that will make it a disease of the past.

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