1. ¹Fred Hutchinson Cancer Research Center, Division of Public Health Sciences, 1100 Fairview Avenue North, MP-381, PO Box 19024, Seattle, WA 98109-1024, USA
2. ²Fred Hutchinson Cancer Research Center, Division of Human Biology, 1100 Fairview Avenue North, MP-381, PO Box 19024, Seattle, WA 98109-1024, USA

Correspondence: Dr CI Li, E-mail: cili@fhcrc.org

Received 10 February 2003; Revised 25 April 2003; Accepted 25 April 2003.

Abstract

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 19.9 kg m^-2. Women whose first tumour was c-erbB-2 positive had a 1.7-fold (95% CI: 1.0–3.0) excess CBC risk. Body mass index and c-erbB-2 expression may be risk factors for CBC in young women. Further observational studies are needed to confirm these findings and to evaluate whether testing for c-erbB-2 in this population may help identify those at high risk for CBC.