SCIENCE: Are Neonics linked to Breast Cancer? | Breast Cancer UK

SCIENCE: Are Neonics linked to Breast Cancer?

Published 23 Mar 2016

Neonicotinoids have been in the press a lot recently because of a general scientific consensus that their use may harm bee populations, but a recent report  suggests that they may also be associated with an increased breast cancer risk.

The report published last week in the journal, Cancer Cell and Microenvironment (1) highlights research which shows low concentrations of neonicotinoid insecticides can lead to an increase in oestrogen production in humans. Higher oestrogen levels are linked to an increased risk of breast cancer (2).

In the study, researchers at the University of Quebec (3) examined expression of the aromatase gene in human cancer cells, and found that neonicotinoids, including thiacloprid and thiamethoxam, increased expression of aromatase, which is a key catalyst for the production of oestrogen. Similarly, exposure to the herbicide, atrazine (now banned in the EU) induces aromatase activity and oestrogen production. High levels of aromatase are found in woman with oestrogen-positive breast cancers (4).

Neonicotinoids are the most commonly used insecticides worldwide, and are applied as seed coatings to protect crops against pests. They are environmentally persistent and have potential to bioaccumulate.

In December 2013, in response to concerns that neonicotinoid seed treatments were responsible for declining bee populations, the European Union imposed temporary restrictions on the use of three neonicotinoid insecticides, including thiamethoxam and imidacloprid which were tested in the study. In July 2015, the restrictions were relaxed temporarily allowing UK farmers to use these insecticides on oil seed rape crops. Currently the European Food and Safety Authority (EFSA) is reviewing the restrictions.

Most studies of endocrine disruption focus on the ability of compounds to act as oestrogen or androgen mimics. The endocrine disrupting effects of neonicotinoids appear to be associated with their ability to increase oestrogen biosynthesis.

The paper by Caron-Beaudoin et al. provides preliminary evidence that neonicotinoid insecticides may increase breast cancer risk and reinforces calls by Pesticide Action Network (PAN) and others, including Breast Cancer UK, for a continuation of imposed restrictions of these insecticides.



1. Caron-Beaudoin, E. and Sanderson, J. T. (2016). Effects of neonicotinoids on promoter-specific expression and activity of aromatase: implications for the development of hormone-dependent breast cancer. Cancer Cell & Microenvironment 3: e1216. doi: 10.14800/ccm.1216.

2. Travis, R. C. and Key, T. J. (2003). Oestrogen exposure and breast cancer risk. Breast Cancer Research 5: 239-247.

3. Caron-Beaudoin, E. et al. (2016). Effects of Neonicotinoids on Promoter-Specific Expression and Activity of Aromatase (CYP19) in Human Adrenocortical Carcinoma (H295R) and Primary Umbilical Vein Endothelial (HUVEC) Cells Toxicological Sciences 149 (1): 134-144.

4. Caron-Beaudoin, E. et al. (2016) op cit

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