GHRH and carcinoid syndrome: Besides the PNENs described above, the other functional hormone-secreting PNENs include “GRFomas”, which generate growth hormone releasing factor (GRF); “ACTHomas”, which secrete ACTH; “PTHrPomas”, which produce parathyroid hormone-related protein (PTHrP); and “PNETs causing carcinoid syndrome”, which secrete serotonin and tachykinins [107].