Very high survival rates have been observed in four through 11 years of follow-up in 4,240 women with a histologically confirmed diagnosis of breast cancer in the Breast Cancer Detection Demonstration Project (BCDDP). The relative five, eight, and 10-year survival rates were 88, 83, and 79 percent, respectively.
Allowances were made for lead-time bias among cancers detected through screening, and the validity of the findings was supported by internal analyses, which showed that length-time bias was of little, if any, importance, and that any possible “overdiagnosis” of cancer cases was also of small relevance. In view of current interest in the value of screening women before age 50, intensive analyses were made comparing the BCDDP data for women in their 40s with women in their 50s. In terms of kinds of breast cancers found, modality of finding them, and survival rates once they have been found, the parallel results for the two groups show that screening was vitually as effective in the younger as in the older women.
Some authorities are of the opinion that the benefits of mammography after age 50 are well documented, but at younger ages the evidence is still inconclusive. The findings in this study show there is no doubt of the very successful results of screening for breast cancer with mammography in younger as well as older women.
In comparing relative five-year and eight-year survival rates for women with invasive breast cancers detected through screening in the BCDDP, with those for cases diagnosed in the National Cancer Institute's Surveillance, Epidemiology and End Results (NCISEER) program from 1977 to 1982, it is seen that for individual subcategories by tumor size and nodal class, the survival rates are about the same. However, for overall invasive cancers, the five-year and eight-year survival rates were 87 and 81 percent, respectively, for the BCDDP, compared with 74 and 65 percent for SEER. Thus the substantial gains in survival followed the large shift toward a high proportion of cancers being diagnosed and treated in more favorable stages through the screening accomplishments.
With respect to the relative case fatality rates, the complements of the relative survival rates, the eight-year rate of 19 percent for the BCDDP versus that of 35 percent for SEER connotes 46 percent fewer women dying in the BCDDP group.