| Abstrakt: |
The objective of the Million Women Study was to asses the risk of breast cancer in users after different regimes of HRT. This was a prospective cohort study on women invited for breast cancer screening. Of those invited, 75% accepted, and 71% (53% overall) of those who accepted actually participated. They ranged in age from 50 to 64 years, recruitment was between 1996 and 2001, with a follow-up from 2.6 to 4.1 years. Mortality was followed up 1- 2 years longer. Information was gathered on history of hormone use. Women were allocated to the hormone group they had when they entered the study. The HRT which was evaluated was the latest one used, irrespective of whether this was the one used longest. Ever use, current use, length of use, age at first use, time since last use and type of hormone used most recently entered the analysis. The average age of women in the study was 55.9 years. There were 9,364 cases of breast cancer and 637 deaths from breast cancer. The risk ratio (RR) for current use of HRT against non-use was 1.66, for past use it was 1.01, and the risk disappeared within one year after cessation. Combined HRT showed a RR estimate of 2. The RR of death of breast cancer is 1.22. Oestrogen-only therapy showed no difference by dose, implants showed an RR of 1.6. The specific estimates on oestrogen types are given. For example, levonorgestrel showed a risk ratio of 1.9 for less than 5 years of use, 2.23 for more than 5 years, but no consistent pattern for differences in risk for sequential and continuous users. Ex-users had no excess risk. The absolute life-time risk of BC is about 10%, and it is 9.7% for never users. The etiological fraction of HRT for BC is approximately 4%. The important messages of this study are that the risk of breast cancer associated with HRT disappears within a year after cessation, and that HRT in general has a modest influence compared with other lifestyle habits. [ABSTRACT FROM AUTHOR] |
