Epidemiologic and molecular risk factors for contralateral breast cancer among young women.

Women diagnosed with a first breast cancer before the age of 45 years have a greater than 5.0-fold risk of developing a second primary contralateral breast cancer (CBC) than women in the general population have of developing a first breast cancer. Identifying epidemiologic or molecular factors that influence CBC risk could aid in the development of new strategies for the management of these patients. A total of 1285 participants in two case-control studies conducted in Seattle, Washington, who were 21-44 years of age when diagnosed with a first invasive breast carcinoma from 1983 to 1992, were followed through December 2001. Of them, 77 were diagnosed with CBC and 907 tumour tissues from first cancers were analysed. Women with body mass indices (BMIs) >/=30 kg m(-2) had a 2.6-fold greater risk (95% CI: 1.1-5.9) of CBC compared to women with BMIs