Factors that increase risk
- Gender. Simply being a woman is the main risk factor for developing breast cancer. Although women have many more breast cells than men, the main reason they develop breast cancer more often is because their breast cells are constantly exposed to the female hormones estrogen and progesterone, which promote cell growth. Men can develop breast cancer, but this disease is about 100 times more common among women than men.
- Age. Your risk of developing breast cancer increases as you age. About 2 out of 3 invasive breast cancers are found in women age 55 or older.
- Family history. The chance of developing breast cancer increases if a close relative, either male or female, had breast cancer. About 20 to 30 percent of women with breast cancer have a family member with the disease.
- Gene changes. Breast cancer is sometimes caused by inherited gene changes. The most common are in the BRCA1 and BRCA2 genes which cause a significantly increased risk for breast and ovarian cancer
- Previous breast cancer. A woman with cancer in one breast is three to four times more likely to develop a new cancer in the other breast, or in another part of the same breast. This is different from a recurrence, or return of the first cancer.
- Benign breast biopsy. About 80 percent of all breast changes that are biopsied, or tested, are found to be benign, or not cancerous. But, some of these benign breast conditions are linked to an increase in breast cancer risk.
- Radiation Exposure. Receiving radiation therapy to the chest between the ages of 10 and 30 can increase the risk of breast cancer. The risk of developing breast cancer appears to be highest if the radiation was given during adolescence, when the breasts are still developing.
- Hormone exposure. Use of hormones after menopause called hormone replacement therapy may increase the risk for developing breast cancer.
Factors that decrease risk
- Age of first birth. Having many pregnancies and becoming pregnant at an early age reduces breast cancer risk. Pregnancy reduces a woman's total number of lifetime menstrual cycles, which may be the reason for this effect.
- Breastfeeding. Some studies have suggested that breastfeeding may slightly lower breast cancer risk. This is more likely if breastfeeding is continued for 1.5 to 2 years or if many children of the same mother are breastfed.
- Staying at a healthy weight. High-fat diets can lead to being overweight or obese, which is a breast cancer risk factor. A diet high in fat has also been shown to influence the risk of developing several other types of cancer.
- Limiting alcohol. The American Cancer Society recommends that women limit their consumption of alcohol to no more than one drink per day to reduce their breast cancer risk.
- Regular physical activity. Evidence is growing that physical activity in the form of exercise reduces breast cancer risk. The only question is how much exercise do you need? In one study from the Women's Health Initiative (WHI) as little as 1.25 to 2.5 hours per week of brisk walking reduced a woman's risk by 18 percent. Walking 10 hours a week reduced the risk even more.
Inherited breast cancer clues
About 10 percent of all breast cancers are due to an inherited gene change. Some clues of an inherited breast cancer risk are:
- Breast cancer diagnosed at age 50 or younger
- Two breast cancers diagnosed in a single individual, or breast and ovarian cancer diagnosed in a single individual
- Having a family history of breast and/or ovarian cancer in two or more relatives on the same side of the family
- Male breast cancer
- Being a member of a family with a known change in a breast cancer susceptibility gene
- Breast cancer in a family with other cancers such as thyroid cancer, pancreatic cancer, and sarcomas
Learn more about our High Risk Breast and Ovarian Cancer Clinics