Chemicals in Medical-Dental Products Linked with Breast Cancer, warn scientists

The increasing use of photo-initiator chemicals in everyday products, especially in medical settings, has raised concerns about their adverse effects on human health. Photo-initiators are endocrine-disrupting chemicals that release reactive molecules in response to UV radiation. Photo-initiator chemicals are present in several objects of everyday use– in a wide range of products, including plastics, paints, inks, and adhesives–as well as in medical products and instruments such as dental fillers and containers–and in instruments used to treat breast cancer patients.

Now scientists have shown that three photo-initiator chemicals — 1-HCHPK, MBB, and MTMP — show estrogen-like activity in mice and increase the growth of breast cancer tumors in these animals. The results warn against the use of such chemicals in medical instruments like containers and call for the prompt development of safer alternatives–especially for treatment of breast cancer patients where use of these chemicals likely means the cure is actually worsening the disease.


Recently, studies have demonstrated several health hazards associated with photo-initiator chemicals, raising alarms about their safety. In particular, the presence of these compounds in clinical instruments, routinely used for treating high-risk individuals such as cancer patients, has become a major cause for concern. Previous studies have shown that three photo-initiator chemicals commonly found in plastics and paints — 1-HCHPK, MBB, and MTMP — show estrogen-like effects on cultured breast cancer cells, increasing their proliferation. Owing to the presence of these compounds in marketed injection solutions and the well-known link between estrogen activity and breast cancer, scientists warn that a thorough investigation of their effect on breast tumor growth is warranted.

Study overview

Scientists examined how exposure to photo-initiator chemicals 1-HCHPK, MBB, and MTMP affected the growth of transplanted breast cancer tumors in mice. They found that all these compounds caused a faster increase in the growth of breast tumors, within 13 weeks of treatment.


“This study extends our previous findings and shows that in addition to promoting the proliferation of breast cancer cells in culture, these photo-initiators also increase the growth of breast tumors in live animals. This implies that they could also potentially hasten disease progression in breast cancer patients.” 

-Dr. Yoichi Kawasaki, lead scientist, Okayama University in Japan


To understand the mechanism underlying these breast tumor-promoting effects, the researchers pre-treated the mice with tamoxifen — a compound that prevents estrogen or estrogen-like molecules from affecting cellular processes. They found that tamoxifen pretreatment substantially decreased the toxic effects of the photo-initiator chemicals, indicating that this toxicity was mediated by estrogen receptors.



“Estrogen promotes the growth of breast cancer tumors. Because tamoxifen blocks estrogen receptors, it is often used in breast cancer treatment. Our results show that the photo-initiators likely promote breast tumor growth by binding to estrogen receptors on tumor cells and initiating estrogen signaling.

-Professor Toshiaki Sendo, researcher, Okayama University in Japan


Study results

Together, the results from the study show that photo-initiator chemicals 1-HCHPK, MBB, and MTMP have estrogen-like activity and could thus act as hormonal disruptions. Given the important role of estrogen in regulating reproductive function in both men and women, such disruptions could affect not only patients with breast cancer, but also healthy individuals…the present study provides information crucial from a breast cancer management perspective and also represents an urgent call-to-action for the elimination of toxic materials from medical equipment.



Journal Reference:  Yoichi Kawasaki, Toshiaki Sendo. Three photoinitiators induce breast tumor growth in mouse xenografts with MCF-7 breast cancer cells. Current Research in Toxicology, 2021; 2: 322.

DOI: 10.1016/j.crtox.2021.08.004