Lean breast adipocytes secrete an oxylipin that suppresses breast cancer via ferroptosis

Obesity is predicted to become the largest modifiable risk factor for breast cancer in postmenopausal women, yet the mechanisms underlying this association are unclear. We identified a novel role for the endogenous oxylipin 9S-HODE, secreted by lean adipocytes, to induce ferroptosis in breast cancer cells while sparing normal breast epithelial cells. Obese adipocytes fail to secrete 9S-HODE, suggesting that the loss of ferroptosis induction significantly contributes to the acceleration of obesity-associated breast cancer. Consequently, the inhibition of ferroptosis accelerates breast cancer in lean, but not obese, mice. Further, 9S-HODE inhibits the growth of patient-derived breast cancer organoids, and supplementing 9S-HODE into tumors in obese mice is sufficient to reduce tumor burden, underscoring its potential as a therapeutic agent.