Aberrant hypothalamic neuronal activity blunts glucocorticoid diurnal rhythms in murine breast cancer

Breast cancer patients often exhibit disrupted diurnal rhythms in circulating glucocorticoids (GCs), such as cortisol. This disruption correlates with reduced quality of life and higher cancer mortality; however, the exact cause of this phenomenon remains unclear. Here, we demonstrate that breast tumor-bearing mice exhibit blunted GC rhythms and a loss of diurnal rhythms in the activity of paraventricular hypothalamic neurons expressing corticotropin-releasing hormone (PVN^CRH). This change in neuronal activity is mediated by disinhibition from upstream GABAergic neurons. Using chemogenetics to stimulate PVN^CRH neurons at different times of day, we show that stimulation just before the light-to-dark transition restores normal GC rhythms, reduces tumor progression, and increases intra-tumor effector T cells (CD8+). Our findings demonstrate that breast cancer distally regulates neurons in the hypothalamus that control the output of the hypothalamic-pituitary-adrenal (HPA) axis and provide evidence that therapeutic targeting of these neurons could mitigate tumor progression via enhancing anti-tumor immunity.