Mammography and clinical examination in mass screening for cancer of the breast

Periodic screening for cancer of the breast using mammography as well as clinical examination is being conducted by the Health Insurance Plan in a large random sample of women aged 40 to 64 years. A similar group of women has been assigned as controls. The long term objective is to determine whether the screening program results in lowering of mortality from mammary cancer. From the first screening examination among 20,211 women, the following observations can be made: 1. Screening has resulted in substantial detection of cancer; mammary cancer is detectable through screening an average of 21 months sooner than usual. 2. A higher proportion of cancers has been detected in the screened group (65%) in an early stage (as shown by the absence of axillary node involvement) than in the control group (41%). 3. Both mammography and clinical examination contribute to the early detection of cancer in mass screening. 4. Mammography and clinical examination are complimentary in detection. 5. Under different conditions of age, breast type and lesion characteristics, the two procedures have different rates of accuracy. 6. Mammography does comparatively well when the woman is older than 50, when the breasts are mostly fatty in type and when the lesion is in the lower half of the breast; clinical examinations do comparatively well when the woman is younger than 50, when the breasts are small and when the breasts are of the glandular type.