Who is at risk of developing breast cancer?

 

In general, breast cancer risk increases as you grow older.

The graph shows age-specific breast cancer incidence rates among women ages 30 and over in California in 1996, the most recent year for which complete data are available. Age-specific rates were calculated by dividing the number of breast cancers diagnosed among women in a five-year age category by the total number of women that age in the state. The graph demonstrates that the risk of developing breast cancer increases with age until about age 80, and then declines.

Of the approximately 20,000 invasive breast cancers diagnosed statewide each year, about five percent are diagnosed among women under the age of 40, 20 percent among women ages 40 to 49, 30 percent among women ages 50 to 64, 35 percent among women ages 65 to 79, and ten percent among women ages 80 and older.

As shown in the graph, white women have the highest incidence of both invasive and in situ breast cancer. The incidence rate is about 20 percent lower among black women, and more than 40 percent lower among Hispanic and Asian/Pacific Islander women.

The reasons for these differences are not well understood, but they are consistently reported in the scientific literature.

However, when rates are examined by the extent to which the cancer has spread when discovered, a somewhat different picture emerges.

 

In the graph, breast cancer incidence rates are shown by stage at diagnosis. Stage 0 tumors are at a very early stage of development, called in situ. Stage I tumors are invasive, but are less than two centimeters in diameter, and have not spread beyond the breast. Stage II, III, and IV tumors are larger or have spread to the lymph nodes or other organs.

Non-Hispanic white and Asian/Pacific Islander women have higher rates of early-stage tumors than later-stage tumors. Hispanic women have about the same rate of early- and later-stage breast cancer, while among black women, rates are higher for later-stage tumors than early stage. Black women are at higher risk for later-stage breast cancer than white women, despite the fact that their overall risk of breast cancer is 20 percent lower.

These differences are critical, because the earlier the breast cancer is discovered, the better the chances are for survival. The higher proportion of breast cancers diagnosed at later-stage among black and Hispanic women may reflect poorer screening, delays in seeking treatment once symptoms are discovered, delays in obtaining medical care and treatment, or differences in tumor biology or risk factors associated with more rapid tumor growth.

Unlike many other cancers, women with more formal education and higher incomes have a higher risk of developing breast cancer than poorer, less educated women. Such measures of socioeconomic status (SES) are probably indirectly related to cancer risk, and represent a constellation of behavioral and lifestyle choices that are yet to be fully understood.

The graph shows invasive breast cancer incidence rates among women age 15 and older in Los Angeles County, comparing rates in the lowest SES group (least educated and poorest) to the highest (best educated and highest income) for women in the four major race/ethnic groups in California. In each race/ethnic group, women in the highest SES group have rates that are about 40 to 60 percent higher than in the lowest SES group.

Having a first-degree relative (mother, sister, or daughter) with a history of breast cancer approximately doubles one’s risk of developing breast cancer.

 

Having a personal history of benign breast disease with atypical hyperplasia can also increase one’s risk.

Other well-established risk factors for breast cancer are thought to relate to lifetime exposure to naturally occurring estrogen levels in the body. Factors that increase lifetime exposure, such as beginning to menstruate before the age of 12, not having children, or going through menopause later in life, tend to increase risk. Having one’s first child after the age of 30 may also increase risk.

It is estimated that well-established risk factors account for, at most, about half of all breast cancers. Many other potential risk factors, such as diet, exercise, and body weight hold tantalizing promise for cancer prevention in the future, because unlike the risk factors mentioned before, they are related to behaviors that we can change.

The National Cancer Institute has developed the Breast Cancer Risk Assessment Tool that women can use to estimate their probability of developing breast cancer based on several recognized risk factors. Information about this software program can be found on the website http://www.nci.nih.gov.