Female breast cancer: facts & figures
|Incidence in Minnesota:|
Breast cancer incidence rates in Minnesota are similar to national trends over time and similar to the national average in recent years. There are geographic differences across Minnesota in incidence rates; the Twin Cities metropolitan area consistently has rates that are higher than the rest of the state.
Breast cancer cases in Minnesota
The risk of developing pre-menopausal breast cancer (defined here as cancer occurring prior to 50 years of age) has been relatively stable over the time period with a 1% annual increase since 2003. The risk of developing post-menopausal breast cancer (defined here as cancer occurring at 50 years and older) has fluctuated considerably; from 2000 to 2004 the rate decreased significantly by 4.7%, and a similar decrease was seen nationally. This decline is generally attributed to a dramatic decrease in the use of post-menopausal hormone replacement therapy following the announcement in 2001 by the National Institutes of Health's Women's Health Initiative (WHI) that hormone therapy increases breast cancer risk. Most recently, the age-adjusted incidence rate of breast cancer was 44.6 new cases per 100,000 females less than 50 years old, 357.2 new cases per 100,000 females aged 50 years and older, and 135.1 new cases per 100,000 females of all ages (combined).
Breast cancer cases and mortality in Minnesota, by race/ethnicity
Female breast cancer incidence is highest among non-Hispanic whites (130.4 new cases per 100,000 females) and lowest among Asian/Pacific Islanders (65.9 new cases per 100,000 females). Mortality is highest among black women, despite their lower incidence rate of breast cancer compared to non-Hispanic white women.
Breast cancer cases in Minnesota, by age
The rate of breast cancer increases with age. Breast cancer is far more common among post-menopausal women.
Breast cancer forms in the tissues of the breast, most commonly beginning in the ducts (tubes that transport milk to the nipple) or lobules (glands that produce milk). Breast cancer can occur in men, but it is rare, accounting for only 0.2% of cancer in men. In contrast, breast cancer is the most common cancer among women, accounting for over 30% of cancers diagnosed. There are about 3,900 new cases of breast cancer diagnosed among women each year in Minnesota.
What are the risk factors for female breast cancer?
There are several well-established risk factors for breast cancer in women, including exposure of the breast tissue to estrogen and family history of breast cancer. However, it is estimated that known risk factors explain less than half the cases of female breast cancer.
- Cumulative exposure of the breast tissue to estrogen (a naturally occurring hormone primarily involved in regulating the menstrual cycle), especially in post-menopausal women. Reproductive factors that increase the exposure of breast tissue to estrogen are those that increase the number of years a woman menstruates: early age at menarche, late onset of menopause, never breast feeding, delayed childbearing, and having fewer or no children. Other established risk factors are thought to increase breast cancer risk because they indirectly increase the amount of estrogen in the blood stream: obesity, higher alcohol consumption, and physical inactivity.
- Combined hormone therapy has been used for many years to relieve symptoms of menopause and decrease the risk of osteoporosis. However, hormone replacement therapy with both estrogen and progesterone increases the risk of breast cancer and the likelihood that the cancer is found at a more advanced stage. A woman's breast cancer risk seems to return to that of the general population within 5 years of stopping combined hormone therapy.
- A family history of breast cancer, especially of pre-menopausal breast cancer. Specific inherited genetic mutations dramatically increase risk and account for between 5-10% of female breast cancers.
- Exposure of the breast to ionizing radiation, especially during puberty, increases risk for breast cancer.
- Use of oral contraceptives slightly increases risk of pre-menopausal breast cancer, but risk returns to normal within ten years after use is discontinued.
How can breast cancer be prevented?
- Individuals can maintain a healthy diet and weight in addition to exercising regularly. Several known risk factors for breast cancer are related to childbearing and breastfeeding, which are personal decisions for women. Women that bear children, breastfeed, and bear children earlier in life have a lower risk of breast cancer because of the association between breast cancer and the cumulative exposure of breast tissue to estrogen.
- Hormone replacement therapy increases breast cancer risk. Get more information about the Women's Health Initiative and Postmenopausal Hormone Therapy from National Institutes of Health (NIH).
- Being regularly screened before symptoms develop does not prevent breast cancer, but it can lead to earlier diagnosis of breast cancer and improve the prognosis (i.e., higher five-year survival). To prevent breast cancer, more research needs to be done to identify new prevention strategies and other important risk factors.
- The Sage Screening Program at MDH is a statewide comprehensive breast and cervical cancer screening program that aims to increase the proportion of women screened for these cancers. The program offers free screening of eligible women (women that meet age, insurance, and income criteria).