Often in medicine, doctors define a range of what’s considered normal. If you’ve ever had bloodwork done, you’ve likely seen this approach at work on the report — your level of platelets or iron or glucose is listed alongside a “normal” range. If your number is outside the defined boundaries for normal, your doctor will usually investigate further to find out why your value isn’t in that range.
With breasts, however, defining normal is a lot harder. Some diagnoses of breast cancer begin with the observation of something about the breast that’s abnormal or different, but because every woman’s breasts are unique, it’s difficult to quantify exactly what a healthy human breast should look like.
Dr. Sara Hurvitz, medical director of the clinical research unit of the Jonsson Comprehensive Cancer Center at UCLA in Los Angeles, says, “Everybody has differences in their breast size and the way that their breasts look. If a woman looks in the mirror, she will likely notice that her breasts are not symmetrical. Some women have an inverted nipple, some have one breast that’s larger than the other. There are so many varieties,” all of which can be completely normal and healthy despite their individual quirks and deviations from what’s accepted as the cosmetic standard these days.
[See: What Not to Say to a Breast Cancer Patient.]
But that’s the outside of the breast, and it’s what’s inside that really counts when we’re talking about breast cancer. Dr. Tari King, chief of breast surgery at Dana-Farber/Brigham and Women’s Cancer Center and the associate division chief for breast surgery at Brigham and Women’s Hospital in Boston, explains that “the breast tissue is made up of milk glands we call lobules and milk ducts, with all those ducts going to the nipple for breastfeeding. In between the milk ducts and the milk glands is fatty tissue. So one can envision it like a bunch of grapes — each grape would be a milk gland, and each stem would be a milk duct. And all those ducts would connect to each other until you got to the main stem that you would hold at the nipple.” The National Cancer Institute hosts a diagram of the human breast on its website that clearly shows what King is describing.
Dr. Harold Burstein, institute physician at Dana-Farber Cancer Institute in Boston and associate professor of medicine at Harvard Medical School, describes the whole system as a “large gland. Obviously, its purpose is to make milk to feed the baby, and many women who’ve been pregnant will remember how the breast swells and the milk fills in.” The breast is a highly changeable part of the body that’s sensitive to monthly changes in hormone levels and responds to pregnancy by expanding to accommodate the milk needed to feed the baby. In some women, this size increase may be minimal while others report jumping three or four bra sizes.
And although providing milk to feed our young is exactly what breasts are intended to do and provide the very definition of what it means to be a mammal, “it’s those glands that make the milk that can give rise to breast cancer,” Burstein says. “Breast cancers begin in the ductal tissue of the breast, the glandular tissue of the breast. Usually when the abnormal cells within the gland begin to grow, they begin by accumulating within the duct. We call that intraductal carcinoma or ductal carcinoma in-situ (DCIS), which is a precancerous lesion, often diagnosed in women who’ve had mammograms. It’s sort of a precursor to breast cancer.”
[See: 16 Health Screenings All Women Need.]
But what makes these tissues so susceptible to developing cancer in the first place? Dr. Parvin Peddi, assistant clinical professor in the division of hematology and oncology at the David Geffen School of Medicine at UCLA in Los Angeles, says the high rate of cell turnover in the breast can contribute to the development of cancer. “Cells are dividing more commonly in the breast, much like stomach tissue or other types of cells do,” and as King explains, the more change that occurs in the tissue, the more chances there are for something to go wrong.
“One of the reasons breast cancer is a common form of cancer is because cancers are more likely to arise in tissue sites or organs that have high levels of proliferation or division and cell turnover. Because cancer is essentially abnormal growth — cells growing in an abnormal manner and the body isn’t stopping them — tissue or organ sites that have high turnover and division and replication to begin with have more opportunity for an error to occur in a rapidly dividing system than elsewhere.”
King says this also happens in the gastrointestinal tract, which is prone to developing cancer, too. “The cancers that arise in the GI tract in the stomach or the colon arise in the cell layer, the epithelial layer that’s constantly being exposed to things in our diet and undergoing constant repair,” she says. “The milk duct cells are also constantly being stimulated by hormonal changes.”
In pre-menopausal women, every month, your hormone levels rise and fall as your body readies itself for a potential pregnancy. Some of those changes occur within the milk ducts in the breast and involve cells proliferating and dividing “in a highly proliferative environment with lots of opportunity for things to go wrong. A division and replication error carried forward by natural process can result in cancer,” King says.
Over time, it’s this constant cellular activity that can cause issues, Peddi says. “Breast tissue goes through so much alteration during a woman’s life. During pregnancy, breastfeeding and all these changes, the cells increase in size and allow a chance for mistakes happen.” Although our bodies are quite adept at squelching these cellular mutations before they turn into cancer, it’s not a perfect system and in some cases, the mistake slips through and a tumor begins to grow.
Hurvitz agrees that the high rate of cell turnover in the breast is likely a contributing factor to why breast cancer is a common affliction, but she says getting a complete answer to the question of what makes breast tissue more susceptible to cancer than some other body tissues is difficult. “We know that there are lifestyle factors related to the development of breast cancer such as prolonged exposure to female hormones. Girls who begin menstruating at an early age or women who enter menopause later have a higher risk,” she says. “Women who don’t become pregnant or do so later in life are also at higher risk. Women who don’t breastfeed also have slightly more risk,” indicating that hormonal exposure is correlated with breast cancer.
Other environmental factors, such as obesity, alcohol intake, diet, exercise level and the use of hormone replacement therapy are also “probably related to the relatively higher incidence,” of breast cancer versus other cancers, Hurvitz says.
[See: A Tour of Mammographic Screenings During Your Life.]
Although there isn’t a lot you can or should do to alter the hormonal changes your body naturally experiences monthly and as you age, staying active, eating right, controlling stress, reducing your alcohol intake and generally leading a healthy lifestyle can all reduce your chances of developing breast cancer. And, you should pay attention to your body and notice any changes in your breasts.
Although no two sets of breasts are alike, Hurvitz says, “after a woman goes through puberty and is in her 20s, she should become familiar with how her breasts look and any new changes in the way the breasts look. If a woman normally has an inverted nipple that begins protruding or one breast is starting to flatten, that’s a change that could highlight a suspicious finding. It’s less important for an individual to know what’s ‘normal’ in all women.” The best advice is to know yourself and what’s normal for you.
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What Makes Breast Tissue Susceptible to Cancer? originally appeared on usnews.com
