Obesity, body fat distribution, and breast cancer risk: is visceral fat the culprit after menopause?

The mechanisms that underlie the emergence of an obesity-associated increased risk in breast cancer after menopause are not fully understood. Increased adipose-derived estrogens certainly contribute to obesity-associated postmenopausal breast cancer, but additional mechanisms are also involved. Most women gain weight during menopause, and this is seen primarily as an increase in visceral adipose tissue (VAT) in the abdominal region. This in turn increases inflammation locally, systemically, and at distant sites such as subcutaneous adipose (SAT) in the breast, suggesting that changes in body composition during menopause could drive increased cancer risk. The long-term goal is to identify the mechanisms underlying obesity-associated tumor risk during menopause, and to use a precisionmedicine approach to develop interventions to effectively minimize this risk in women with obesity. The overall objective of this grant is to determine the functional role that menopausal VAT deposition plays in obesity-related breast cancers. The central hypothesis is that increased VAT deposition during menopause mediates breast tumor development and growth through increased production of adipokines, cytokines, and growth factors that signal systemically to metabolically activate a subset of tumor-promoting macrophages in the mammary adipose/breast. Using a well-characterized preclinical rat model of obesity and postmenopausal breast cancer combined with a syngeneic orthotopic transplant model and in vitro assays, the central hypothesis will be tested with the following specific aims: 1) Determine the functional contribution of menopause-induced visceral adipose accumulation on mammary tumor development; 2) Interrogate how modifying insulin resistance, VAT, and adiposederived signals alters macrophage activation, and the resulting impact on tumor development and growth after OVX. Preclinical findings will be confirmed in relevant clinical samples. The research proposed in this application is highly innovative as it will directly assess the biological role of visceral fat, inflammation, insulin resistance, and associated metabolic activation of macrophages in the tumor promotion process. Further, it will define a specific macrophage subtype that could be targeted to decrease obesity-associated cancers after menopause. This is significant as it will identify new targets for future pharmacological therapies and will provide the foundational platform for a precision medicine approach, using a clearly measurable target (decreased VAT), during a critical life stage (perimenopause/ menopause), to decrease cancer risk in women with obesity.