DESCRIPTION: This application for a competitive renewal of "Factors that affec survival of young breast cancer patients", seeks to extend for five more years the follow-up for recurrence and mortality of a population-based cohort of 128 women who were diagnosed with invasive breast cancer before age 45 during the years 1983 through 1992. These women provide the investigators with a unique opportunity to investigate the interrelationships between epidemiologic risk factor data, tumor characteristics, and breast cancer occurrence and/or mortality in a population-based setting where all cases of breast cancer in a defined geographic area could be assessed, eliminating potential biases impose by studies at referral centers or clinical trials, where women may self-select into the study and not be representative of women in general who get breast cancer. During the past five years, this cohort was followed through follow-up questionnaires and hospital chart reviews, and their tumor specimens were tested for characteristics related to aggressiveness and prognosis. It is important to extend follow-up of this cohort to a minimum of ten years since patient and tumor characteristics may have different relationships with short and long-term mortality. During the next five years, the investigators propose to (a) expand data collection and specimen analyses to the entire cohort (rather than the subgroup of 930 they originally proposed), (b) extend the minimum follow-up period for the entire cohort to ten years, (c) collect updated information on recurrences, treatment, the use of hormone replacement therapy and childbearing after diagnosis, (d) add apoptotic index to the laboratory analyses, and (e) conduct comprehensive analyses of all of these data in relation to mortality and disease-free survival. Young women with many years of potential life to lose who do not fall into clear prognostic categories present a major challenge to clinicians. By gainin an understanding of the association between epidemiologic risk factors and tumor characteristics related to aggressiveness as well as actual risk of recurrence or death, it is possible to develop profiles of women at high risk for aggressive tumors who might benefit from aggressive treatment and of those with low risk tumors for whom such aggressive treatment may not be necessary.