Objective: To determine the positive predictive value (PPV) of low-cost screening mammography according to age and family history of breast cancer.
Design: Cross-sectional.
Setting: Six counties in northern California.
Participants: A total of 31,814 women aged 30 years and older referred for mammography to the University of California, San Francisco, Mobile Mammography Screening Program from April 18, 1985, through November 20, 1992.
Measurements: Breast cancer risk profile, two standard mammographic views per breast, and follow-up of abnormal screening examinations.
Results: Although women aged 50 years or older constituted only 38.3% of all women who received first-screening mammography, 74% of breast cancers were detected in this group. Ten cancers were diagnosed per 1000 first-screening examinations in women aged 50 years or older, with 14.8 diagnostic procedures per cancer diagnosed compared with two cancers per 1000 screening examinations and 48.3 diagnostic tests per cancer diagnosed in women younger than 50 years. The PPV of first-screening mammography (number of breast cancers detected per abnormal examination) increased with age: .03 for those aged 30 to 39 years; .04 for those aged 40 to 49; .09 for those aged 50 to 59; .17 for those aged 60 to 69; and .19 for those aged 70 years or older (chi 2 for trend, P < .001). Women aged 50 to 59 years had a higher PPV for first-screening mammography than women aged 40 to 49 years (.09 vs. .04; P = .004), and women with a family history of breast cancer had higher PPVs compared with women without history (40 to 49 years of age, .13 vs .04, P = .01; and 50 to 59 years of age, .22 vs .09, P = .01).
Conclusion: Five times as many cancers per 1000 first-screening mammographic examinations were diagnosed in women aged 50 years or older compared with women aged less than 50 years. The highest PPVs for mammography were in women aged 50 years or older and in women aged 40 years or older with a family history of breast cancer. Efforts to promote screening mammography should focus on women in these groups, in whom the majority of breast cancers occur and for whom mammography has the highest PPVs.