Probability of Breast Cancer in American Women

by National Cancer Institute

Key Points

The National Cancer Institute estimates that, based on current rates, 13.2 percent of women born today will be diagnosed with breast cancer at some time in their lives.

Because rates of breast cancer increase with age, estimates of risk at specific ages are more meaningful than estimates of lifetime risk.

An estimated risk represents the average risk for all women in the United States as a group. This estimate does not indicate the risk for an individual woman because of individual differences in age, family history, reproductive history, race/ethnicity, and other factors.

Estimated lifetime risk of breast cancer has gone up gradually over the past several decades. This year it declined slightly.

The National Cancer Institute's (NCI) Surveillance, Epidemiology, and End Results (SEER) Program has published its SEER Cancer Statistics Review 1975-2002. This report estimates that, based on current rates, 13.2 percent of women born in the United States today will develop breast cancer at some time in their lives. This estimate is based on cancer statistics for the years 2000 through 2002.

This estimate means that, if the current rate stays the same, women born now have an average risk of 13.2 percent (often expressed as "1 in 8") of being diagnosed with breast cancer at some time in their lives. On the other hand, the chance that they will never have breast cancer is 86.8 percent (expressed as "7 in 8").

In the 1970s, the lifetime risk of being diagnosed with breast cancer in the United States was just under 10 percent (often expressed as "1 in 10"). The estimated lifetime risk has generally been rising gradually since then; this year, the estimated risk decreased slightly.

The last five annual SEER reports show these estimates of lifetime risk:

13.2 percent for 1996 through 1998 ("1 in 7.55," often expressed as "1 in 8")

13.4 percent for 1997 through 1999 ("1 in 7.45," often expressed as "1 in 7")

13.5 percent for 1998 through 2000 ("1 in 7.40," often expressed as "1 in 7")

13.4 percent for 1999 through 2001 ("1 in 7.47," often expressed as "1 in 7")

13.2 percent for 2000 through 2002 ("1 in 7.56," often expressed as "1 in 8")

Because of rounding to the nearest whole number, a small decrease in the estimated risk in this year's SEER report (a decrease from "1 in 7.47" to "1 in 7.56") led to the change from "1 in 7" to "1 in 8."

SEER statisticians expect some variability from year to year. Slight changes, such as the one reported this year, may be explained by a variety of factors, including minor changes in risk factor levels in the population, slight changes in screening rates, or just random variability inherent in the data.

The estimated probability of being diagnosed with breast cancer for specific age groups and for specific time periods is generally more informative than lifetime probabilities. Estimates by decade of life are less influenced by changes in life expectancy and incidence rates. The SEER report estimates the risk of developing breast cancer in 10-year age intervals. These calculations factor in the proportion of women who live to each age. In other words, they take into account that not all women live to older ages, when breast cancer risk becomes the greatest. A woman's chance of being diagnosed with breast cancer is:

from age 30 through age 39	0.44 percent (often expressed as "1 in 229")
from age 40 through age 49	1.46 percent (often expressed as "1 in 68")
from age 50 through age 59	2.73 percent (often expressed as "1 in 37")
from age 60 through age 69	3.82 percent (often expressed as "1 in 26")

These probabilities are averages for the whole population. An individual woman's breast cancer risk may be higher or lower, depending on a number of factors, including her family history, reproductive history, race/ethnicity, and other factors that are not yet fully understood. To calculate an individual's estimated risk, see the Breast Cancer Risk Assessment Tool at http://www.cancer.gov/bcrisktool/ on the Internet.

About the Author

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