This lack of heterogeneity in disease in young women accords with the analysis of Yasui and Potter (1999), who applied the age-specific distribution of ER/PR subtypes seen in tumours of 3359 cases (of all ages) in the Danish Breast Cancer Cooperative Group to the national Danish age-specific breast cancer incidence rates (age was the only risk factor examined in their analysis). Here, PGR is linked to breast cancer.