Researchers in Pennsylvania have found what may be part of the mechanism by which breast cancer grows and develops. This culprit is a hormone that normally comes from the brain, but can be produced at any of a number of sites throughout the body. This hormone promotes cell growth, but sometimes gets out of control.
It’s called prolactin, and its main function is to regulate lactation. Prolactin has a variety of functions, however—over 300, potentially with more yet undiscovered—and is found in some non-mammals, animals that don’t lactate. In men prolactin is part of the process by which sperm is formed. The hormone helps regulate the immune system, including preventing a pregnant woman from having an immune reaction to the fetus. It also helps regulate clotting.
Almost all of the body’s prolactin is produced in the pituitary gland in the brain. But prolactin can come from a variety of tissues, though this extra-pituitary prolactin isn’t necessarily used by the body in the same way. Some prolactin is actually produced right in the breast tissue. Scientists aren’t currently sure why this happens. It doesn’t always appear to have any effect on lactation or milk production, but it does seem to have the same effect on cells that prolactin produced in the pituitary gland ordinarily does.
Because prolactin promotes cell growth, it has been a target of research into cancer causes and treatments. Around 14 years ago, it was discovered that prolactin encourages the growth not only of healthy cells, but also breast cancer tumors. Patients with breast cancer are sometimes found to have elevated levels of prolactin, whereas healthy people almost never do. Now researchers have found some evidence that the growth of tumors in breast tissue actually stimulates the production of prolactin in the breast itself. This prolactin in turn speeds tumor growth. In this way, the tumor cells actually hijack the body to perpetuate and protect themselves. This means attacking prolactin production outside the pituitary gland may be an effective attack on breast cancer.