The Role of Chewing and Chronic Stress in Breast Cancer Progression and Metastasis: A Review

Chronic stress is defined as a prolonged state of emotional disturbance and psychological strain resulting from an inability to maintain internal homeostasis. It is recognized as a significant risk factor for breast cancer, primarily through the chronic activation of the sympathetic nervous system and the hypothalamic–pituitary–adrenal (HPA) axis. This neuroendocrine activation leads to elevated systemic levels of epinephrine, norepinephrine, and glucocorticoids. By binding to their respective adrenergic and glucocorticoid receptors, these hormones disrupt immune homeostasis and exacerbate oxidative stress within the tumor microenvironment. Such physiological shifts promote critical oncogenic processes, including angiogenesis and tumor cell proliferation, thereby driving the development, progression, and distant metastasis of breast cancer. Mastication, or the act of chewing, serves as a practical and effective behavioral strategy for modulating the deleterious effects of chronic psychological stress. Recent animal studies have provided compelling evidence that chewing can attenuate excessive stress responses. Specifically, it has been shown to mitigate stress-induced breast cancer progression and metastasis by modulating the expression of stress hormones, their corresponding receptors, and key downstream signaling pathways. These findings suggest that the rhythmic activity of chewing may exert a protective effect against stress-related tumor exacerbation. Consequently, further clinical research is warranted to determine whether chewing interventions can serve as a viable complementary strategy alongside conventional breast cancer prevention and treatment protocols.