INSL5 and breast cancer: Collectively these tissues of expression correlate well with current hypotheses that INSL5 a) is a gut hormone that modulates glucose metabolism either directly or indirectly via gluconeogenesis (6–8); b) is an orexigenic hormone that influences satiety, through both gut-nervous system and hypothalamus-cerebellum cross-talk with RXFP4 (9); c) plays roles in female and male fertility (6, 10, 11), and d) together with RXFP4, are markers of colorectal and breast cancer progression (12–15).