Rising incidence of breast cancer among young women in Sweden.

The national Swedish cancer registry was used to analyse the age-specific time trends in breast cancer incidence in Sweden from 1970 to 1984. The analysis included both a calendar year and a birth cohort approach to estimate time trends in disease occurrence. According to the birth cohort approach there was a statistically significant increase in the incidence with an average annual increase of the incidence of 3.2% (P = 0.0114), 3.4% (P = 0.0002) and 2.2% (P = 0.0264) in the age groups 25-29, 30-34 and 35-39, respectively. Possible causes of the observed increasing incidence are discussed.