Is a dense mammographic parenchymal pattern a contraindication to hormonalreplacement therapy?

The aim of the study was to And out whether the effect of hormonal replacem ent therapy (HRT) is modified by the mammographic parenchymal patterns on t he risk of breast cancer. Subjects were 4163 Finnish women aged 40-47 years at entry who were invited to breast cancer screening every second year fro m 1982 to 1990. Mammographic parenchymal patterns (Wolfe's classification) were recorded at each screening round. The information. on use of HRT, was recorded From 1984. The follow-up ended in 1993 and up until that time 68 n ew breast cancers were diagnosed. A Poisson regression model was used in th e analysis of the data. Use of HRT was not related to the risk of breast ca ncer (RR = 0.7. 95% CI 0.4-1.4), whereas mammographic parenchymal pattern w as statistically significantly associated with risk of breast cancer. The a ge-adjusted relative risk of breast cancer among women with PZ versus N1 pa ttern was 2.5 (95% CI 1.3-4.8) and with DY versus N1 pattern 4.9 (95% CI 1. 6-15.1). Women using HRT and with DY pattern were at substantially increase d risk of breast cancer (RR = 11.6. 95% CI 2.5-53.6) compared with women no t using HRT and with N1 pattern. There was an increased risk of breast canc er among women with DY mammographic parenchymal pattern who used HRT. which was consistent with a synergistic joint effect.