EFFICACY OF SCREENING MAMMOGRAPHY - A METAANALYSIS

Objective.-To determine the efficacy of screening mammography by age, number of mammographic views per screen, screening interval, and durat ion of follow-up. Design.-Literature review and meta-analysis. Data Id entification and Analysis.-Literature search of English-language studi es reported from January 1966 to October 31, 1993, using MEDLINE, manu al literature review, and consultation with experts. A total of 13 stu dies were selected, and their results were combined using meta-analyti c techniques based on the assumption of fixed effects. Main Results.-T he overall summary relative risk (RR) estimate for breast cancer morta lity for women aged 50 to 74 years undergoing screening mammography co mpared with those who did not was 0.74 (95% confidence interval [CI], 0.66 to 0.83). The magnitude of the benefit in this age group was simi lar regardless of number of mammographic views per screen, screening i nterval, or duration of follow-up. In contrast, none of the summary RR estimates for women aged 40 to 49 years was significantly less than 1 .0, irrespective of screening intervention or duration of follow-up. T he overall summary RR estimate in women aged 40 to 49 years was 0.93 ( 95% CI, 0.76 to 1.13); the summary RR estimate for those studies that used two-view mammography was 0.87 (95% CI, 0.68 to 1.12) compared wit h 1.02 (95% CI, 0.73 to 1.44) for those studies that used one-view mam mography, and for those studies with 7 to 9 years of follow-up, the su mmary RR estimate was 1.02 (95% CI, 0.82 to 1.27) compared with 0.83 ( 95% CI, 0.65 to 1.06) for those studies with 10 to 12 years of follow- up. Conclusion.-Screening mammography significantly reduces breast can cer mortality in women aged 50 to 74 years after 7 to 9 years of follo w-up, regardless of screening interval or number of mammographic views per screen. There is no reduction in breast cancer mortality in women aged 40 to 49 years after 7 to 9 years of follow-up. Screening mammog raphy may be effective in reducing breast cancer mortality in women ag ed 40 to 49 years after 10 to 12 years of follow-up, but the same bene fit could probably be achieved by beginning screening at menopause or 50 years of age.