VIP and ptosis: Other clinical syndromes, such as intractable diarrhea, which mayoccur when neoplastic cells produce vasoactive intestinal peptide (VIP), andHorner’s syndrome, which is characterized by unilateral ptosis, miosis andanhidrosis (usually associated with tumors in the upper thoracic or cervicalregion), also have a low incidence - 3.1 and 2.0%, respectively.21