Preface.

Breast cancer (BC) is the most frequently diagnosed malignancy in young women and is the leading cause of cancer-related mortality in this age group. This issue represents a major public health problem in developing countries, where the incidence of BC is rapidly increasing and where young women represent a higher proportion of the total BC patient population compared to developed countries. In Latin America, BC among women aged 40 years or less accounts for up to 11% of new BC cases and 7% of all BC deaths. In Mexico, a very high proportion of the total number of BC patients are diagnosed in their early years, reaching up to 15% in some healthcare institutions.