Does a relationship exist between trends in estrogen receptor levels and breast cancer incidence and mortality?

Estrogen receptor data from 4,049 patients with primary breast cancer treated at the National Cancer Institute of Naples between 1984 and 1996, have been evaluated to analyze temporal trend of this tumor marker. The prevalence rate of estrogen receptor levels falls from >75% in women older than 60 years to <70% in younger patients. The analysis of these data by birth cohort shows a trend very similar to that of breast cancer incidence in Italy, suggesting that the breast cancer appearance could be modulated in different period of life.