Breast cancer (BC) has become a major public health problem in Latin America (LA), as it is the most common form of cancer among women. In Women are more likely to develop BC at younger age, and to be diagnosed at an advanced stage compared to western women. Over the past twenty years, the mortality from BC in LA has also been increasing very rapidly, and is currently the leading cause of cancer mortality among LA women. The large number of incident BC cases among premenopausal women, which is only partly explained by the population age-structure, is therefore of major concern. Little is known on specific risk factors for premenopausal BC in general, and in LA in particular, and risk factors related to diet, obesity and low physical activity play a role on incidence and mortality. Estrogen receptor (ER) and/or Progesterone receptor (PR) expression in breast tumors may differ according to risk factors and to molecular pathological characteristics. There is a lack of specific knowledge on tumor molecular and pathological characteristics of BC in premenopausal women, particularly in lower resource countries where the hormone-dependence status is poorly documented. This has major consequences on cancer treatment and survival.