Gender: women; women are 100 times more likely to have breast cancer than men (ACS, 2004f)

Personal history of breast cancer: increased risk of developing a new breast cancer, particularly in the contralateral breast (ACS, 2004f)

Previous abnormal breast biopsy: 1.5 to 2 times increased risk if previous biopsy results had any of the following changes: fibroadenoma with complex features, hyperplasia without atypia, sclerosing adenosis, solitary papilloma; 4 to 5 times increased risk if results were atypical hyperplasia (ductal or lobular); no increased risk if results were "fibrocystic changes without proliferative breast disease" or "fibroadenoma" (ACS; 2004d; ACS, 2004f)

Previous chest irradiation: previous radiation treatment for other types of cancer (e.g., Hodgkin's Disease, non-Hodgkin's lymphoma; ACS; 2004d; ACS, 2004f)

Long menstrual history or lifetime endogenous estrogen exposure: early menarche (i.e., before age 12) and late menopause (i.e., after age 55; ACS; 2004d; ACS, 2004f)

Obesity: overweight women were 60% more likely to die from breast cancer than were normal-weight women (Calle et al., 2003); a higher risk of breast cancer has been associated with weight gain after menopause (Lahmann, Lissner, Gullberg, Olsson, & Berglund, 2003); data on breast cancer risk for women who have been overweight since childhood is not as clear at this time (ACS, 2004d)

NOTE: A summary of other factors, for which preliminary data suggest an association with breast cancer risk, can be found on the "Additional resources & References" page.

Based on cancer statistics for 1999 through 2001, 13.4 percent of women born now in the United States will develop breast cancer at some time in their lives (Reis et al., 2004).

• This average risk is often expressed as: 1 in 7 women will develop breast cancer at some time in their lives.
• This lifetime risk has increased gradually since the 1970s when it was 10% or expressed as 1 in 10 women.

Risk assessment may be more easily understood by identifying the average risk that a woman has of developing breast cancer within a specific age decade (National Cancer Institute, 2005e).

A woman's chance of being diagnosed with breast cancer:
    from age 30 to age 40 . . . is 0.44% or 1 in 227 women
    from age 40 to age 50 . . . is 1.49% or 1 in 67 women
    from age 50 to age 60 . . . is 2.79% or 1 in 36 women
    from age 60 to age 70 . . . is 3.83% or 1 in 26 women

These risk estimate rates are averages for the population of women as a whole. This estimate is less influenced by life expectancy and incidence rates (National Cancer Institute, 2005e). An individual woman's risk for breast cancer may be higher or lower depending on a number of factors (e.g., family history and reproductive history).

Risk assessment tools (i.e., Gail and Claus) are available to determine a woman's lifetime risk of developing breast cancer, but have not been validated in minority populations and can underestimate risk for women with a family history of hereditary breast cancer.

A comparison of these screening tools is available on the National Cancer Institute web site, Genetics of breast and ovarian cancer - Models for prediction of breast cancer risk (2005d)

The breast cancer risk assessment tools can be used to help determine recommendations for screening and are available at:

1. Breast Cancer Risk Assessment Tool (National Cancer Institute) based on the Gail Model (Klausner, Kramer, & Gail, 1998) The NCI tool is based on the Gail Model for 5 Year Risk of Breast Cancer
2. Claus Model (Claus, Risch, & Thompson, 1994)

Additional information about lifetime risk can be found in the NCI fact sheet: Calculating lifetime risk of breast cancer: Questions and answers

For more information on the lifetime risk of developing or dying from breast cancer, see Cancer control and population sciences - Surveillance research.