SURVIVAL ADVANTAGE DIFFERENCES BY AGE - EVALUATION OF THE EXTENDED FOLLOW-UP OF THE BREAST-CANCER DETECTION DEMONSTRATION PROJECT

Background. This study considers breast cancer survival patterns by ag e group among women diagnosed in the Breast Cancer Detection Demonstra tion Project (BCDDP) to provide insight into the nature of breast canc er and suggest a possible explanation as to why the results of the ran domized clinical trials differ for women younger than 50 and those 50 or older. Based on the findings of several randomized clinical trials, there is a general consensus that breast cancer screening provides a significant benefit for women aged 50-69. From these trials, there is little evidence of a short term benefit and uncertainty regarding any long term benefit of mammographic screening for women aged 40-49. Meth ods. The BCDDP was not a randomized trial, but a nationwide breast can cer screening program conducted between 1973-1980, in which all partic ipants received annual physical and mammographic examinations. Using t he BCDDP data, this study calculated 14-year breast survival among 405 1 women diagnosed with cancer between 1973 and 1980 and followed throu gh 1988 and 1989. Results. In all, 598 women died of breast cancer, re sulting in an overall 14-year breast cancer survival of 83.4% (standar d error = 0.007). Breast cancer survival varied by tumor type, lymph n ode status, tumor size, and stage at diagnosis. For most of the cases, however, both the distribution and breast cancer survival rates were similar for women aged 40-49, 50-59, and 60-69 across all prognostic i ndicators. Only breast cancer survival among women with invasive breas t cancer who had a primary tumor 5 cm or larger or with positive lymph nodes differed by age, with women aged 60-69 at diagnosis having poor er survival. Analyses by modality of detection conducted in a subset o f 2739 cases indicated that the 34.6% of the cases detected by mammogr aphy alone had the highest overall breast cancer survival rates (90.9% ), while the 32.2% of the cases detectable by both physical examinatio n and mammography had the lowest breast cancer survival (79.0%). Overa ll, women diagnosed with breast cancer in the BCDDP had a survival adv antage if diagnosed with either a smaller tumor or no positive lymph n odes, or if their breast cancer was detected by mammography alone. For women with large tumors (greater than or equal to 5 cm), the survival was 80.8% for ages 40-49, 72.1% for ages 50-59, and 61.7% for ages 60 -69. Discussion. Due to the higher breast cancer survival rates among women aged 40-49 with poorer prognostic characteristics, the breast ca ncer survival advantage for having a smaller tumor, no positive lymph nodes, or breast cancer detected by mammography alone was lower for wo men aged 40-49 than women aged 50 or older at diagnosis. These differe nces in survival advantage may help to account for the differences in mortality by age in the randomized clinical trials.