From the article:
After all, triple negative breast cancers lack estrogen receptors (along with progesterone receptors and HER2, thus the name triple negative), and so these cancers can’t possibly be influenced by estrogen. Right?
[…]
Technically, Cittelly and colleagues including postdoctoral researcher, Maria Contreras-Zarate, PhD, found that estrogen induces astrocytes (brain cells) to produce growth factors called brain-derived neurotrophic factor (BDNF) and Epidermal Growth Factor (EGF), and that these factors turns on two genetic migration/invasion switches in cancer cells, namely TRKB and EGFR.
“This may explain why breast cancers diagnosed in younger women are more likely to metastasize to the brain – pre-menopausal women have more estrogen, and it may be influencing the microenvironment of the brain in ways that aid cancer,” Cittelly says.