EFFECT OF AGE, BREAST DENSITY, AND FAMILY HISTORY ON THE SENSITIVITY OF FIRST SCREENING MAMMOGRAPHY

Objective.-To determine factors that influence the sensitivity of mode rn first screening mammography. Design.-Cross-sectional. Setting.-Nine counties in northern California. Participants.-A total of 28 271 wome n aged 30 years and older referred for first screening mammography to the Mobile Mammography Screening Program of the University of Californ ia, San Francisco, from April 1985 to March 1 992, of whom 238 were su bsequently diagnosed as having breast cancer. Measurements.-Breast can cer risk profile, 2 standard mammographic views per breast, breast den sity, and follow-up of abnormal and normal mammography by contacting w omen's physicians and by linkage to the regional Surveillance, Epidemi ology, and End Results tumor registry to determine the occurrence of a ny invasive cancer or ductal carcinoma in situ. Results tumor registry to determine the occurrence of any invasive cancer or ductal carcinom a in situ. Results.-For women aged 50 years and older, the sensitivity of first screening mammography was relatively high and decreased slig htly with increasing length of follow-up after mammography: 98.5% for 7 months of follow-up, 93.2% for 13 months, and 85.7% for 25 months. S ensitivity was higher among women aged 50 years and older when breast density was primarily fatty rather than primarily dense (98.4% vs 83.7 %; P<.01). For women younger than 50 years, the sensitivity of first s creening mammography also decreased with increasing length of follow-u p but was significantly lower than for older women: 87.5% for 7 months of follow-up, 83.6% for 13 months, and 71.4% for 25 months. For women younger than 50 years, breast density did not affect the sensitivity of mammography (81.8% for those with primarily fatty breasts vs 85.4% for those with primarily dense breasts) and was lower among those with a family history of breast cancer (68.8%). Conclusions.-The sensitivi ty of modem mammography is highest among women aged 50 years and older who have primarily fatty breast density. Sensitivity is lowest among women younger than 50 years and particularly low when the time between screenings is about 2 years or when women have a family history of br east cancer, possibly because of rapid tumor growth.