Fertility drugs do not increase the risk of developing breast cancer, a UK study has shown.

Using records from 1.8 million women who received fertility treatment in the last 30 years, researchers from King's College London assessed whether routinely used fertility drugs increase breast cancer risk.  

'Fertility treatment can be an emotional experience. Patients often ask us if taking ovarian stimulating drugs will put them at increased risk of developing cancers, including breast cancer,' said study author Dr Yusuf Beebeejaun from King's Fertility. 'To answer that important clinical question, we undertook this review that reports data from nearly 2 million people.'

The study, published in Fertility and Sterility is the largest of its kind ever carried out. The researchers analysed patient records from 1990 to 2020, including women of all reproductive ages who were followed up for an average of 27 years after undergoing fertility treatments. The participants, all of whom had no previous history of breast cancer, were treated with ovulation stimulants gonadotrophins and/or clomiphene citrate. 

The study reported no significant increase in breast cancer risk to women treated with either drug alone or in combination when compared to both healthy and infertile untreated women.

'Our study showed that the use of drugs to stimulate ovaries in fertility treatment did not put women at increased risk of breast cancer,' said senior author Dr Sesh Sunkara, lecturer in women's health at King's. 'This study provides the evidence needed to reassure women and couples seeking fertility treatments.'

Fertility drugs stimulating the release of eggs from a patient's ovaries have been used since the early 1960s and can be part of a range of fertility treatments including IVF. Both investigated drug types - clomiphene and gonadotrophins – stimulate the production of follicles in the ovaries, which contain the eggs. Alongside, ovulation stimulation medication typically increases the production of oestrogen, a hormone that can act on breast cells. Researchers were concerned that this effect could increase the risk for breast cancer formation in treated women.

Dr Kotryna Temcinaite from the charity Breast Cancer Now, said: 'Previously it was unclear whether fertility drugs affect breast cancer risk, and we do receive calls to our helpline from women who are concerned that their breast cancer has been caused by fertility treatment. While this analysis of existing published studies does provide welcome reassurance that fertility treatment is unlikely to increase breast cancer risk, further long-term and detailed studies are now needed to confirm these findings.' 

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