It has been known for about ten years that some oestrogen/progestin menopausal hormone therapies (MHT) are associated with an increased risk of breast cancer. Studies have nonetheless suggested that this risk is rapidly attenuated or even eliminated in 2-5 years if the patients stop their treatment. However, questions remain regarding this attenuation, and its relationship to the initial duration of treatment and with the types of drugs administered. The Inserm “Nutrition, Hormones and Women’s Health” team at the Centre for Research in Epidemiology and Population Health (U1018, CESP, Villejuif) has studied these questions using data from the E3N cohort.
In a study published last April, the researchers succeeded in showing that women given MHT remain at higher risk of getting breast cancer several years after finishing their treatment compared with women who have never had MHT.
This risk would apply only to women who have been treated for a long period, i.e. longer than 5 years, with a combined MHT that includes oestrogen and a progestin other than micronised progesterone or dydrogesterone.
“Our study shows that if the risk of getting breast cancer is twice as high for women at the time of treatment, it remains 1.4 times as high in the 5 years following interruption of treatment, and for 5-10 years after. After 10 years following cessation, the risk remained higher for women who had been treated, but the results were based on insufficient numbers and insufficient statistical significance,” explains Agnès Fournier.
The team concludes this study by saying that “additional studies are needed,” to find out exactly how long this excess risk persists over time.
Since its beginnings in 1990, the E3N cohort study has received sustained support from the French National Cancer League and its departmental committees. Besides the League, the other three founding partners are Inserm, Gustave Roussy Institute and MGEN (mutual insurance company). IReSP (French Public Health Research Institute) helped to fund the present project.