Standardized methods and questionnaires have been developed and implemented as well as standard operating procedures for laboratory activities. Incident primary invasive cases aged 20-45 years are recruited from major cancer hospitals in four large Latin American cities (Mexico City, San Jose, Medellin, and Santiago) prior to any treatments. Controls for the study are selected from the population residing in the same cities for at least 3 years and matched to cases on age (+/- 5 years) and health care institution. For each subject, complete questionnaire data on socio-demographic factors, health history, reproductive history, use of hormones, early risk factors, body silhouette at different ages, physical activity, diet, occupation, environmental risk factors, ethnicity, and family history of cancer are collected. Validated and standardized food frequency questionnaires are administered to gather information on diet. Anthropometry (body weight, standing and sitting height, waist and hip circumferences) are measured according to standardized protocols. Blood and urine samples are also collected for biomarker analyses. For all cases, highly standardized immunohistochemical and molecular analyses are performed to identify BC subtypes.