Drugs used during fertility treatments to release eggs do not increase the risk of developing breast cancer, a study shows.

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.

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.

'Patients often ask us if taking ovarian stimulating drugs will put them at increased risk of developing cancers, including breast cancer. .

Researchers addressed the association between the use of ovarian stimulation drugs (pictured in stock image) and the risk of developing breast cancer.

The problem is that drugs that are used to stimulate the ovaries increase oestrogen hormone production and can act on breast cells. 

There has been concern that this could turn the cells cancerous, which has led to an uncertainty about the potential risk of infertility drugs causing breast cancer

Researchers found no significant increase in breast cancer risk for women exposed to treatment compared to untreated women, both fertile and infertile

No significant increase in the risk of breast cancer was found with the use of clomiphene citrate or gonadotropins, alone or in combination.     

'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 Dr Sesh Sunkara, senior-author of the paper, from King's College London. 

Dr Kotryna Temcinaite at UK charity Breast Cancer Now, has called for more research into what factors do contribute to someone's risk of developing breast cancer. 

'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,' said Dr Temcinaite, who was not involved in the new study. 

'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.'