Drugs routinely used during fertility treatment to stimulate ovaries to release eggs are not associated with an increased risk of developing breast cancer, new UK-led research has shown.
The systematic review and meta-analysis, published in Fertility and Sterility journal, is the largest study to date to examine the association between the use of ovarian stimulation drugs and risk of breast cancer. As these drugs increase oestrogen production and can act on breast cells, there has been concern about their potential to increase the risk of breast cancer in women who have undergone fertility treatment.
Researchers from King’s College London, in partnership with King’s Fertility, analysed cohort studies (1990-2020) involving 1.8 million women without any previous history of breast cancer undergoing ovarian stimulation. Women of all reproductive ages were included in this study and followed up for an average of 27 years following their fertility treatment.
Overall, the quality of evidence was very low because of the serious risk of bias and indirectness (non-randomised studies).
However, there was no significant increase in the risk of breast cancer among women treated with any ovarian stimulation drug for infertility compared with that in unexposed controls from the general population and infertile population (pooled OR, 1.03; 95% CI, 0.86-1.23; 20 studies; I2, 88.41%; very low quality of evidence).
Furthermore, no significant increase in the risk of breast cancer was found with the use of clomiphene citrate or gonadotropins, alone or in combination.
“Although this study provided reassuring evidence, it highlights the need for further register-based studies with the potential to span longer follow-up periods, the provision of a detailed infertility treatment history, and adjustment for confounding factors so as to avoid the additive effect of infertility,” the study authors concluded.
