Breast cancer is the most commonly diagnosed cancer among women in the world. In the U.S., skin cancers are the leading diagnosed cancer in women, with breast cancer coming in second, according to the American Cancer Society.
While the disease may occur in anyone with breast tissue, there are risk factors that can increase a person’s chances of getting a disease, but having one or more breast cancer risk factors does not determine the outcome. Breast cancer risk factors may be unrelated to personal choices or associated with a specific lifestyle, and not all risk factors are accepted by medical experts.
Risk Factors Unrelated to Personal Choices
Gender and Age
Both men and women can suffer from breast cancer, but women are far more likely to develop it than men, according to the American Cancer Society. The higher incidence of breast cancer among women is thought to be related to a higher amount of the two female hormones, estrogen and progesterone, that are known to fuel the growth of breast cancer cells. Similarly, a woman’s risk of developing breast cancer increases with age. The ACS estimates that about 1 in 8 women will develop invasive breast cancer.
The ACS says that from 5 to 10 percent of breast cancer cases are probably hereditary, resulting from gene defects called mutations. In hereditary breast cancer, the most common cause is an inherited mutation in the BRCA1 and BRCA2 genes. “In normal cells, these genes help prevent cancer by making proteins that keep the cells from growing abnormally,” the ACS website says. “If you have inherited a mutated copy of either gene from a parent, you have a high risk of developing breast cancer during your lifetime.”
But the risk varies, and while a mutation in the BRCA1 gene may increase the lifetime risk of breast cancer by as much as 80 percent, the average increase is between 55 and 65 percent. The average increased risk related to BRCA2 mutations is about 45 percent. Other rare genetic mutations are also known to contribute to inherited breast cancer, including mutations in the ATM, TP53, CHEK2, PTEN, CDH1, STK11, and PALB2 genes.
Family and Personal History
Given the correlation between genetics and breast cancer, the risk is more significant in women with close blood relatives who have had the disease. Having a first-degree relative, like a mother, sister, or daughter with breast cancer can double the risk, while having two first-degree relatives with the disease can triple the risk. There is less information about a male relative with breast cancer, and the degree of risk here is unknown, although it exists. Altogether, about 15 percent of breast cancer patients have a family member who has or had the disease.
Similarly, a women who suffered from and was treated for breast cancer has a higher risk of suffering from a new cancer in another part of the same breast or in the other breast.
Race and Ethnicity
The ACS notes that white women are slightly more likely to develop breast cancer than African-American women, but black women are more likely to die of the disease. But in women younger than 45, breast cancer is more common in black women.
“Asian, Hispanic, and Native-American women have a lower risk of developing and dying from breast cancer,” the ACS reports. Also, BRCA mutations have different incidences depending on race and ethnicity. “In the United States, BRCA mutations are more common in Jewish people of Ashkenazi (Eastern Europe) origin than in other racial and ethnic groups, but they can occur in anyone.”
Dense Breast Tissue
The breast is composed of fatty tissue, fibrous tissue, and glandular tissue. In a mammogram, physicians are able to analyze the density of breast tissue, which means the amount of each type of tissue. A woman is considered to have dense breast tissue when there are high amounts of glandular and fibrous tissue, and low fatty tissue.
According to the American Cancer Society, having dense breasts increases the risk of cancer between 1.2 and two times, compared to women with average breast density. A number of factors can affect breast density, including menopause, age, medication such as menopausal hormone therapy, pregnancy, and genetics. Dense breast tissue can also make mammograms less accurate.
Benign breast diseases can also increase the risk of developing breast cancer. The probability is different according to the disease, which is why benign breast conditions are usually divided into three general groups. Nonproliferative lesions refer to fibrosis and/or simple cysts, mild hyperplasia, adenosis (non-sclerosing), ductal ectasia, phyllodes tumor (benign), single papilloma, fat necrosis, periductal fibrosis, squamous and apocrine metaplasia, epithelial-related calcifications, or other benign tumors, and these are not associated with overgrowth of breast tissue, affecting breast cancer risk to a very small extent.
Proliferative lesions without atypia include usual ductal hyperplasia (without atypia), fibroadenoma, sclerosing adenosis, papillomatosis, and radial scar, and they cause excessive growth of cells in the ducts or lobules of the breast tissue, increasing the risk of breast cancer by 1.5 to two times. Proliferative lesions with atypia are atypical ductal hyperplasia (ADH) and atypical lobular hyperplasia (ALH), and they result in an overgrowth of cells in the ducts or lobules of the breast tissue, with some of the cells no longer appearing normal, increasing the risk of breast cancer by 3.5 to five times.
Other diseases not included in these three groups that impact the development of breast cancer are mastitis, an infection of the breast, and lobular carcinoma in situ (LCIS), a type of noninvasive breast cancer that increases the risk of additional breast tumors by between seven and 11 times.
Women who began menstruating early — before age 12 — or who go through menopause later in life, after age 55, have had a higher number of lifetime menstrual cycles than other women, which slightly increases the risk of breast cancer. This is thought to be related to a longer exposure to the female sex hormones estrogen and progesterone.
Drugs and Treatments
Women who had radiation therapy to the chest area as treatment for another cancer such as lymphoma when they were children or young adults have a significantly increased risk for breast cancer, the ACS states. The risk varies with the patient’s age when they had radiation, and whether they also had chemotherapy, which may halted ovarian hormone production for some time. That would lower the risk.
“The risk of developing breast cancer from chest radiation is highest if the radiation was given during adolescence, when the breasts were still developing. Radiation treatment after age 40 does not seem to increase breast cancer risk,” the ACS says.
For several decades — from the 1940s through the 1960s — some pregnant women were given the drug diethylstilbestrol (DES) because physicians thought it would lower their chances of miscarriage. Risk factors are slightly higher in these women, too, as well as women whose mothers took DES during pregnancy.
Risk Factors Related to Lifestyle
Having Children and Breastfeeding
Not having children or having a first child after the age of 30 is known to slightly increase the risk of breast cancer, while multiple pregnancies beginning at a younger age reduces the overall risk of breast cancer. Still, pregnancy is different for every woman, and types of breast cancer differ as well. Pregnancy, for instance, is thought to increase the risk of a breast cancer called triple-negative. Breastfeeding has been shown in research to lower the risk of breast cancer, particularly if it is continued for 1.5 or two years. This is thought to be related to a reduction in a woman’s total number of lifetime menstrual cycles.
According to the ACS, women who take oral contraceptives are at a slightly higher risk of developing breast cancer than women who never took birth control pills. But the risk tends to normalize with time as women stop taking the pills, and is thought to be nonexistent 10 years after women stop taking them.
Another birth control form, depot-medroxyprogesterone acetate (DMPA, or Depo-Provera), which is an injectable form of progesterone given once every three months, is also thought to increase the risk, but not at a truly relevant level if the drug was last used more than five years ago.
Hormone Therapy After Menopause
Estrogen and progesterone are often used as hormone therapy to help ease the symptoms of menopause and prevent osteoporosis. This treatment goes by many names, such as post-menopausal hormone therapy (PHT), hormone replacement therapy (HRT), and menopausal hormone therapy (MHT).
Two main types of hormone therapy are used, depending on whether a woman still has her uterus or if she has undergone a hysterectomy. Studies have demonstrated that using combined hormone therapy after menopause increases the risk of getting breast cancer, as well as the risk of dying from breast cancer. The use of estrogen alone after menopause does not appear to increase the risk of developing breast cancer.
Alcohol Use and Smoking
“The use of alcohol is clearly linked to an increased risk of developing breast cancer. The risk increases with the amount of alcohol consumed,” the ACS says. “Compared with non-drinkers, women who consume one alcoholic drink a day have a very small increase in risk. Those who have two to five drinks daily have about 1½ times the risk of women who don’t drink alcohol.” the American Cancer Society explains.
For many years, researchers found no connection between cigarette smoking and breast cancer. But in recent years, studies have shown that long-term heavy smoking is linked to a higher risk of breast cancer, the ACS states. “Some studies have found that the risk is highest in certain groups, such as women who started smoking before they had their first child,” the group states.
Weight and Exercise
Before menopause, ovaries produce most of the estrogen and fat tissue produces a small amount. After menopause, the ovaries stop producing estrogen, and the only estrogen production comes from the fat tissue. As a result, being overweight or obese after menopause increases breast cancer risk. Also, women who are overweight tend to have higher blood insulin levels, which is connected to breast cancer risk.
Physical activity and exercise decrease the risk of breast cancer. According to a study from the Women’s Health Initiative, 1.25 to 2.5 hours of brisk walking each week is able to decrease a person’s risk by 18 percent.
Controversial Risk Factors
Diet and Vitamin Intake
Numerous studies focused on the correlation between diet and breast cancer risk, but the results are not definitive. While some research indicated an impact for diet, others found no evidence that diet influences breast cancer risk.
“For example, a recent study found a higher risk of breast cancer in women who ate more red meat. Studies have also looked at vitamin levels, again with inconsistent results,” the ACS says. “Some studies actually found an increased risk of breast cancer in women with higher levels of certain nutrients.” The truth is, no studies have shown that vitamins reduce the risk of breast cancer. Of course, a healthy diet is still important. There are benefits to a diet high in fruits and vegetables, and low in fat, red meat and processed foods.
There is a possible correlation between chemicals present in the environment and risk of breast cancer. The impact is still not clear, but investigators have focused on compounds with properties similar to estrogen, including substances present in certain plastics, cosmetics and personal care products, pesticides (such as DDE), and PCBs (polychlorinated biphenyls). Some poeple have suggested concern over the chemicals in antiperspirants that may be absorbed into the skin. However, there is little scientific evidence to support this hypothesis.
Some studies demonstrated that women who work night shifts, like nurses, are more likely to suffer from breast cancer, but the reasons for this are not fully understood. “This is a fairly recent finding, and more studies are looking at this issue. Some researchers think the effect may be due to changes in levels of melatonin, a hormone whose production is affected by the body’s exposure to light, but other hormones are also being studied,” the American Cancer Society says.
Note: Breast Cancer News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.