Drugs used during fertility treatments to release eggs do not increase the risk of developing breast cancer, a study shows.
Researchers from King's College London analysed studies involving 1.8 million women undergoing fertility drug treatments.
The women, all of whom had no previous history of breast cancer, were followed up in studies for an average period of 27 years.
Researchers found they showed 'no significant increase' in the risk of developing breast cancer compared to those who hadn't taken the drugs.
The research is the largest study to date assessing whether commonly used fertility drugs are a cancer risk for women, researchers say.
Pictured, syringe and needle to inject gonadotropins, a fertility medication. No significant increase in the risk of breast cancer was found with the use of gonadotropins or clomiphene citrate, alone or in combination, the King's College London team reveal
'Fertility treatment can be an emotional experience,' said study author Dr Yusuf Beebeejaun from King's College London.
'Patients often ask us if taking ovarian stimulating drugs will put them at increased risk of developing cancers, including breast cancer.
'To answer that important clinical question, we undertook this review that reports data from nearly 2 million people.'
Fertility drugs to stimulate ovaries to release eggs have been used to treat infertility since the early 1960s.
All the women within the study used either two types of ovulation induction medication, or a combination of both – clomiphene and gonadotrophins.
Both types of drug are marketed worldwide under a variety of brand names.
Gonadotrophins are hormone agents that can be given in an injection to stimulate a woman's ovaries to produce follicles, which contain an oocyte (egg).
Researchers addressed the association between the use of ovarian stimulation drugs (pictured in stock image) and the risk of developing breast cancer
Clomiphene, a synthetic chemical that's taken orally, binds to estrogen receptors in the brain and boosts levels of follicle-stimulating hormone (FSH), which itself is a type of gonadotrophin.
Both clomiphene and gonadotrophins are used as part of an in vitro fertilisation (IVF) treatment to stimulate ovaries.
IVF involves stimulating a patient's ovarian cycle, extracting eggs from their ovaries, fertilising them with sperm in a laboratory and then transferring the embryo into the womb to develop.
'While IVF is a process, ovarian stimulation is the first and most important part of the process,' Dr Beebeejaun told MailOnline.
'The use of the agents that were looked within this review at are the medications that women will use to stimulate their ovaries to produce more eggs.
'These eggs will then be retrieved and fertilised and embryos transferred, as part of the
