Hormones, smoking and mammographic density in postmenopausal Norwegian women : the Tromsø Mammography and Breast Cancer Study

Abstract

Breast cancer is the most commonly occurring malignancy among women, and according to estimates by the International Agency for Research on Cancer, more than one million new cases were diagnoscd worldwide in 2002 (1). In Norway, altogether 2,780 women were diagnosed with breast cancer in 2005, corresponding to an age-adjusted (world) incidence rate of 75.7 per 100,000 women per year (2). According to the predictions for the years 2010-2020 by the Cancer Registry of Norway, we can expect a continued increase in breast cancer incidence, resulting in more than 4,000 new cases annually by the year 2020 (estimated to >80 breast caneer cases per 100,000 women per year) (2). About 80% of new breast cancers cases are diagnosed in women 50 years or older. Although breast cancer mainly affects older women, the predicted increase in breast cancer incidence is only partly explained by the change in age distribution to older women (2). Thus, other risk factors than age must be of importance.