Giving birth may influence the risk of getting certain types of breast cancer according to recent research
When a breast cancer patient has their tumor biopsied or removed, a pathologist will take a sample of the removed cancer cells and will test them for receptors for estrogen, progesterone, or for HER2. The results of these tests will help determine the best treatment for the patient and the overall prognosis (or chance of recovery).
Receptors are proteins that help cells communicate with the outside world. When a receptor binds a specific molecule, various processes within the cell are triggered. For example, when estrogen binds to estrogen receptors and progesterone binds to progesterone receptors normal cellular processes involved in cell growth and division are triggered. However, in breast cancer, one of both of of these receptors are overproduced triggering breast cells to grow and divide rapidly, which eventually leads to the development of a tumor or cancerous growth. Relatively recently it has been discovered that another receptor, HER2- which seemingly does not have any molecules which bind it naturally- is also overproduced in some breast cancers. HER2 overproduction also tells breast cancer cells to grow and divide rapidly, also leading to tumor growth.
Most breast cancers have one or more of these receptors; however one type, called triple negative breast cancer does not have any of them.
Tumors that that have estrogen receptors generally respond well to treatment with antiestrogens, which prevent estrogen binding the estrogen receptors and triggering growth of breast cancer cells. Likewise, tumors that have HER2 generally respond well to trastuzumab, more commonly known as Herceptin, which stops HER2 triggering growth of breast cancer cells. However, triple negative breast cancers seem to be more difficult to treat and has a higher chance of the cancer coming back (recurrence). In addition, a large proportion of these tumors contain the BRCA1 mutation; a genetic fault which generally signifies an increased risk of a women getting breast cancer in her lifetime.
Hormone levels change during pregnancy, with estrogen being produced by the placenta throughout a pregnancy until birth. Because triple negative breast cancers, don’t have any estrogen receptors and hormone levels change during pregnancy, it is thought that childbirth could influence the risk of getting this type of breast cancer.
To address this question, Phipps and colleagues at the Fred Hutchinson Cancer Center in New York used data from over 150,000 women enrolled in the Women’s Health Initiative, a large study of postmenopausal women from 40 centers across the United States. 155,723 women were monitored over 8 years. Of these women, breast cancer developed in 6,194 women and complete data on estrogen receptor, progesterone receptor, and HER2 status was available in 307 women who developed triple-negative breast cancer, 2,610 women with estrogen receptor positive breast cancer, and the remaining cancers were estrogen receptor negative/progesterone receptor positive or estrogen receptor negative/progesterone receptor negative/HER2 positive (n=154). 150,529 women were used as controls.
They found that women without children had an increased risk of estrogen receptor positive breast cancer, but decreased risk of triple-negative breast cancer compared to those who had given birth to children. Specifically, having not given birth to children was associated with a 39% lower risk of triple negative breast cancer, but a 35% higher risk of estrogen receptor positive breast cancer compared with women who had given birth to children. For the statistically minded, see full statistics below. However, of those women who had given birth, those with more children had a higher risk of triple-negative and lower risk of estrogen receptor positive breast cancer (see below).
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