What causes breast cancer?
-Certain factors, called risk factors, increase the likelihood that a woman will develop breast cancer.
-Many of these risk factors are not reversible, but some can be modified.
Not all factors increase a woman's chance of developing breast cancer equally.
Some factors increase a woman's risk of breast cancer more than others
The presence of breast cancer risk factors does not mean that cancer is inevitable: many women with risk factors never develop breast cancer.
Instead, risk factors help to identify women who may benefit most from screening or other preventive measures.
Average woman: 10 to 15% chance of developing breast cancer if she lives into her 90s.
The risk of developing breast cancer in a woman with a strong family history of the disease who has inherited one of the genes that predispose her to breast cancer is over 50%
Unlike lung cancer, for which smoking is the biggest and most powerful risk factor, there is no single factor that is responsible for the majority of breast cancers in women.
Nevertheless, there are 3 factors that strongly increase a woman's risk of developing this disease:
Advancing age
Family history of the disease
Personal history of breast cancer
Primary risk factor for breast cancer is older age
Overall, 85% of cases occur in women 50 years of age and older
Only 5% of breast cancers develop in women younger than age 40
Family history of breast or ovarian cancer are at a higher risk for breast cancer
Women who have an especially strong family history (eg, 2 or more first-degree relatives [a mother, daughter, or sister] with breast or ovarian cancer, particularly before menopause) have a greater than 50% chance of developing breast cancer.
One of the main factors responsible for this elevated risk is an inherited genetic mutation in one of 2 genes, called BRCA1 and BRCA2.
Women who have had cancer in one breast have an increased risk of developing cancer in the other breast.
This is especially true if a woman has an inherited BRCA mutation.
Factors can modestly increase a woman's risk of developing breast cancer
Density of the breasts on mammogram
Biopsy abnormalities
Exposure to radiation
Density of the breasts on mammogram
Women whose mammograms show many dense areas of tissue have an increased risk of breast cancer compared to women whose mammograms reveal mainly fat tissue.
A woman who is told that her mammogram has areas of increased density should ask her healthcare provider to explain what this means
Women who have had a prior breast biopsy that revealed a proliferative abnormality (excessive growth of the glandular breast tissue) have an increased risk for breast cancer, particularly if the cells appear abnormal
Benign breast conditions that are not proliferative (eg, fibrocystic change, or a noncomplex fibroadenoma) do not increase the risk of a woman developing breast cancer.
Women who have undergone high-dose radiation therapy to the chest region, usually as part of cancer treatment, have an increased risk for breast cancer
Several other factors can increase a woman's risk of developing breast cancer.
Many of these factors are related to exposure to a hormone, estrogen.
None are very powerful risk factors
Age at time of reproductive events
During a woman's reproductive years, estrogen stimulates cells of the breast's glandular tissue to divide.
The longer a woman is exposed to estrogen, the greater her risk for breast cancer.
Estrogen exposure is increased if a woman began menstruating at or before 11 years of age, or if she experiences menopause at age 55 years or older
Pregnancy and breastfeeding
Women who have never given birth are more likely to develop breast cancer after menopause
The timing of a first pregnancy also appears to play a role; women who have their first full-term pregnancy at the age of 30 years or older have an increased risk of breast cancer as compared to women who give birth before age 30
Hormone replacement therapy (HRT)
As a woman ages, the breast's glandular tissue, the tissue in which breast cancer arises, is gradually replaced by fat.
HRT includes estrogen, which slows or reverses this process.
Studies have shown that long-term use of combined estrogen-progestin (approximately 5 years) in women ages 50 to 79 increases a woman's risk of breast cancer, as well as heart disease, stroke, and clots in the legs.
Obese women are more likely than thin women to develop breast cancer
Women who drink alcohol have an increased risk of breast cancer, perhaps due to elevated levels of estrogen in the body.
The more alcohol a woman drinks, the greater her risk.
Presence of other cancers
Women who have been diagnosed with cancer of the endometrium, ovary, or colon are more likely to develop breast cancer than women who do not have these cancers.
Studies have shown that,
Women of high socioeconomic status are more likely than women of low socioeconomic status to develop breast cancer
Women who live in urban settings are more likely than women who live in rural settings to develop breast cancer
Some studies support an association between exposure to light at night (such as with night shift work) and the risk of breast cancer, but the strength of the association has been variable.
Black women are more likely than Asian women to develop breast cancer before the age of 40 years
White (non-Hispanic) women are more likely than Asian women to develop breast cancer at the age of 40 years and older
Women who smoke also appear to have an increased risk of breast cancer
SUMMARY
Age and health history can affect
the risk of developing breast cancer
Risk factors for breast cancer include the following:
Older age
Menstruating at an early age
Older age at first birth or never given birth
A personal history of breast cancer or benign (non-cancerous) breast disease
A mother or sister with breast cancer
Treatment with radiation therapy to the breast/chest
Breast tissue that is dense on a mammogram
Taking hormones such as estrogen and progesterone
Drinking alcoholic beverages
Other risk factors
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