A study by Goodson et al, published in the journal Carcinogenesis, found that treating breast cells with BPA led to marked resistance to rapamycin, which is used to treat breast cancer. Also, breast cells treated with either BPA or methylparaben (commonly used as a preservative in cosmetics and some medications) counteracted the beneficial anti-estrogenic effects of tamoxifen.

Overall, these xenoestrogens (a synthetic or natural hormone that imitates estrogen), when tested in benign breast cells from multiple human subjects, consistently initiated specific functional changes of the kind that are attributed to malignant onset in breast tissue.

The study concluded that their observations reinforce the concern that BPA and methylparaben, at low concentrations detected in humans, can have adverse health consequences.