Exploratory investigation of the correlation between microplastics and breast cancer: Polystyrene-derived microplastics promote cell proliferation via estrogenic endocrine disruption

Polystyrene-derived microplastics (PS-MP) are one of the most important environmental problems in modern society and are associated with various chronic disorders. Previous studies have shown that PS-MP exerts estrogenic effects on aquatic organisms. This research indicates that PS-MP may function as an endocrine-disrupting chemical and a risk factor for estrogen-related diseases, such as breast cancer. However, the carcinogenic potential of PS-MPs in breast cancer has not been studied extensively. Therefore, in the present study, we aimed to elucidate the effects of PS-MP on human breast cancer cells. Estrogen receptor (ER)-positive (MCF-7) and ER-negative (MDA-MB-231) human breast cancer cells were exposed to low and high concentrations of PS-MP for 4 weeks. MCF-7 cells exposed to PS-MP exhibited significantly increased cell viability, whereas MDA-MB-231 cells showed no change. Subsequent in vitro and in vivo experiments demonstrated that PS-MP-stimulated MCF-7 cells significantly increased non-genomic ER signaling pathways and tumor growth in mice. Moreover, the ER-knockdown MCF-7 cells were not affected by PS-MP simulation. Our results demonstrate that PS-MP stimulation promotes the malignant transformation of human breast cancer cells via the ER signaling pathway. Considering the emerging concerns regarding PS-MP pollution worldwide, these data provide novel insights into the potential carcinogenic risk of PS-MP to human breast cancer.