A study by Darbre and Harvey, published in the Journal of Applied Toxicology, found that parabens can enable development in human breast epithelial cells of four of six of the basic hallmarks if cancer, one of two of the emerging hallmarks and one of two of the enabling characteristics.

In Hallmark 1, parabens have been measured as present in 99% of human breast tissue samples, possess estrogenic activity and can stimulate sustained proliferation of human breast cancer cells at concentrations measurable in the breast.

In Hallmark 2, parabens can inhibit the suppression of breast cancer cell growth by tamoxifen.

In Hallmark 3, parabens give a dose-dependent evasion of apoptosis (cell death) in high-risk donor breast epithelial cells.

In Hallmark 4, long-term exposure (>20 weeks) to parabens leads to increased migratory and invasive activity in human breast cancer cells, properties that are linked to the metastatic process. As an enabling characteristic parabens can cause DNA damage at high concentrations.

For more on parabens and breast cancer, see here.