This population-based case-control study was conducted from 2000-2003 in two major cities in Poland, Warsaw and Lodz, and enrolled 2,386 breast cancer cases and 2,798 age and site matched controls. This large population-based study combines state-of-the art techniques of exposure assessment and collection of biological specimens to allow for the study of a wide range of biomarkers. Exposure information is obtained through detailed personal interviews, anthropometric measurements, physical activity monitors, and collection of dust samples from the participants’ homes. The collection of biological specimens includes blood samples processed as cryopreserved whole blood, serum+ blood clot, plasma+buffy coat+red blood cells; 12-hour overnight urine; paraffin embedded tumor and normal tissue; and fresh tissue from tumors, non-neoplastic breast tissue and mammary fat tissue. We obtained five year follow-up information from medical records for approximately 1,300 breast cancer cases recruited in Warsaw and 300 cases recruited in Lodz, as well as mortality data on most cases in the study using the Cancer Registry and Death Certificate Office database in Poland. The main research projects being conducted include: Analyses of questionnaire-based factors and anthropometric/physical activity measurements in relation to cancer risk and clinical outcomes; identifying genetic susceptibility markers of cancer risk and clinical outcomes using candidate gene and genome-wide association (GWAS) approaches; analyses of breast tissue/tumor markers to evaluate relationships with cancer risk factors (known or suspected), and their impact on predicting recurrence and survival after diagnosis; and analyses of biomarkers in DNA (somatic changes), cryopreserved blood cells, serum/plasma, and urine in relationship to cancer risk and clinical outcomes