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Scientists identify 900 chemicals linked to breast cancer

An analysis of official databases containing tens of thousands of common chemicals used daily in food, consumer products and other industries, has identified 900 chemicals linked to breast cancer – either via animal or laboratory studies.

Women are most commonly exposed to the breast cancer-causing chemicals via pesticides used on fruit and vegetables, and in cosmetic products, like anti-wrinkle cream, makeup, shampoo and soap, reports Daily Mail. Worldwide, female breast cancer is the fifth leading cause of death, killing nearly 700 000 women in 2020.

Toxicologist and lead researcher of the study Dr Jenny Kay, from Silent Spring Institute in Massachusetts, USA, appealed to regulators to phase out dangerous chemicals and replace these with alternatives.

In the United States, breast cancer is the most common cancer, with about 240 000 cases diagnosed annually, and over the past few years, there has been a rise in cases among younger women – under 50 – which doctors say cannot be explained by genetics.

For the study, published in the journal Environmental Health Perspectives, the team searched databases of tens of thousands of chemicals, including those run by the International Agency for Cancer Research (IACR), the National Toxicology Programme and the US Environmental Protection Agency (EPA).

They searched for chemicals that had been linked to the development of mammary tumours, or breast cancer, in animals, and for chemicals known to activate the production of oestrogen, with high levels of this hormone being a known risk for breast cancer.

They ended up with a list of 922 chemicals they suggest could raise the risk of breast cancer.

About 278 of these had been linked to mammary tumours in animals, and another 420 were found to both damage DNA and alter hormones, making them even riskier.

The list included the pesticides atrazine and malathion – two of the most widely used in the United States.

Pesticides may raise the risk of cancer by triggering gene mutations that raise the risk a cell will start to divide uncontrollably.

There were also numerous chemicals used in hair dyes, like 1,4-Benzenediamine, and in cosmetic products including retinol cream, and in soaps, shampoos and shaving foam – octyl gallate – on the list.

The researchers’ list also included common medications like aspirin, while they suggested prednisone could raise the risk of breast cancer: the drug is prescribed to more than 25m people every year for treating arthritis, among other things.

Doctors have previously suggested aspirin could reduce the risk of breast cancer and of the disease recurring, although this was not backed by clinical trials.

On the list were also several chemicals used in paints and plastics, such as packaging and laptop covers.

Kay said the study aimed to raise awareness about the widespread common chemicals which could increase breast cancer risk – and to prompt action from regulators.

“The biggest surprise was just how few chemicals in daily use in the country have been screened by the EPA for breast cancer risk.

“They have looked at fewer than 2 300 of them – out of tens of thousands. There is a concerningly large group that hasn’t been checked.”

Study details

Application of the Key Characteristics Framework to Identify Potential Breast Carcinogens Using Publicly Available in Vivo, in Vitro, and in Silico Data

Jennifer Kay, Julia Green Brody, Megan Schwarzman,, and Ruthann Rudel.

Published in Environmental Health Perspectives on 10 January 2024


Chemicals that induce mammary tumours in rodents or activate oestrogen or progesterone signalling are likely to increase breast cancer (BC) risk. Identifying chemicals with these activities can prompt steps to protect human health.

We compiled data on rodent tumours, endocrine activity, and genotoxicity to assess the key characteristics (KCs) of rodent mammary carcinogens (MCs), and to identify other chemicals that exhibit these effects and may therefore increase BC risk.

Using authoritative databases, including International Agency for Research on Cancer (IARC) Monographs and the US Environmental Protection’s (EPA) ToxCast, we selected chemicals that induce mammary tumours in rodents, stimulate oestradiol or progesterone synthesis, or activate the oestrogen receptor (ER) in vitro. We classified these chemicals by their genotoxicity and strength of endocrine activity and calculated the overrepresentation (enrichment) of these KCs among MCs. Finally, we evaluated whether these KCs predict whether a chemical is likely to induce mammary tumours.

We identified 279 MCs and an additional 642 chemicals that stimulate oestrogen or progesterone signalling. MCs were significantly enriched for steroidogenicity, ER agonism, and genotoxicity, supporting the use of these KCs to predict whether a chemical is likely to induce rodent mammary tumours and, by inference, increase BC risk. More MCs were steroidogens than ER agonists, and many increased both estradiol and progesterone. Enrichment among MCs was greater for strong endocrine activity vs. weak or inactive, with a significant trend.

We identified hundreds of compounds that have biological activities that could increase BC risk and demonstrated that these activities are enriched among MCs. We argue that many of these should not be considered low hazard without investigating their ability to affect the breast, and chemicals with the strongest evidence can be targeted for exposure reduction. We describe ways to strengthen hazard identification, including improved assessments for mammary effects, developing assays for more KCs, and more comprehensive chemical testing. 


EHP article – Application of the Key Characteristics Framework to Identify Potential Breast Carcinogens Using Publicly Available in Vivo, in Vitro, and in Silico Data (Open access)


Daily Mail article – Women are exposed to nearly a thousand chemicals linked to breast cancer on an almost daily basis, a study has found (Open access)


See more from MedicalBrief archives:


US lawsuit claims L’Oreal’s hair straighteners caused cancer


Suncreens containing toxins still available on shelves despite warnings


Call for calm after ‘cancer-causing chemicals’ alarm


Thousands of black women sue over cancer from hair products claims


Uterine cancer risk linked to hair-straightening products – US study










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