Are younger women with breast cancer more likely to develop another primary cancer later in life as compared to their older counterparts? According to some experts, younger women may have more unfavorable tumor characteristics. Others hypothesize this increase is observed because younger women can be observed for longer periods. To better understand this phenomenon, Dr Lene Mellemkjaer, senior researcher at the Institute of Cancer Epidemiology of the Danish Cancer Society in Copenhagen, Denmark, and colleagues conducted a study of 304,703 women who received a diagnosis of breast cancer between 1943 and 2006 according to registries in Denmark, Norway, and Finland.