CCK and breast cancer: Estrogen and progesterone are the hormones that primarily influence breast cancer, while Cholecystokinin (CCK, a key hormone that inhibits stomach emptying and stimulates midgut motility in gastric species) is involved in pancreatic cancer development, where researchers have found the CCK-receptor expressed in pancreatic cancer cells (14, 15), in the same way that the estrogen and progesterone receptors are present on the surface of many cell types, including those of the breast (16).