A breast cancer risk-prediction model developed for African-American women underpredicted individual risk and risk of estrogen receptor (ER)–negative disease in a large study.

The model, based on data obtained from the Women’s Contraceptive and Reproductive Experiences (CARE) study, has been validated in women aged 50 years or older, but not in younger women or for specific breast cancer subtypes, explained Deborah A. Boggs, ScD, of the Slone Epidemiology Center at Boston University in Boston, Massachusetts, and colleagues in Journal of the National Cancer Institute. The team set out to validate the CARE model in the ongoing Black Women’s Health Study (BWHS), using data from 45,942 women who were aged 30 to 69 years at baseline.

Boggs and her team identified 852 invasive breast cancers during a mean follow-up of 9.5 years. The CARE model predicted 749.6 breast cancers, which translated to an expected-to-observed (E/O) ratio of 0.88. The E/O ratio did not appreciably differ between women younger than age 50 years and those older.

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The greatest underprediction of risk was seen among women who were aged 25 years or older when their first child was born: The CARE model underestimated the number of breast cancers in this group by 29% (E/O = 0.71). However, the model was found to be well calibrated among women younger than age 25 years at birth of first child. Women’s age at first birth is not used in the CARE model; Boggs’s group suggested that including this factor may improve the tool’s performance.

More women in the BWHS than in the CARE study gave birth to their first child at a later age. Breast cancer incidence also was higher in the BWHS compared with national rates used in the CARE model.

The CARE model was worse at predicting ER-negative breast cancer than ER-positive disease. As noted in a statement from Boston University Medical Center, ER-negative breast cancer, which is more aggressive than the ER-positive form, disproportionately affects African-American women.

Boggs and coauthors also found that similar to other breast cancer risk-prediction models, the CARE model was unreliable in predicting a woman’s individual risk of developing breast cancer.