Breast Cancer

Breast cancer is considered a major health problem in western countries, and indeed it constitutes the most common cancer among women in the European Union [48]. A study developed in $2003$ by the American Cancer Society estimates that in the United States between one in eight and one in twelve women will develop breast cancer during their lifetime [1]. This proportion is reduced in our country, Catalonia, where it is estimated that one in sixteen women will develop breast cancer during their lifetime [58].

In the European Community, breast cancer represents $19\%$ of cancer deaths and the $24\%$ of all cancer cases [47]. Nearly $25\%$ of all breast cancer deaths occur in women diagnosed between ages $40$ and $49$ years. In the United States, for instance, breast cancer remains the leading cause of death for women in their forties [21].

However, although breast cancer incidence has increased over the past decade, breast cancer mortality has declined among women of all ages [162]. This favourable trend in mortality reduction is considered to be related to the widespread adoption of mammography screening [3,39,71,162,170,176] which allows to detect the cancer at its early stages, and to the improvements made in breast cancer treatment [21].