Conditions Necessary for Clinical Syndromes	

It is important to clarify the conditions that determine the development of clinical syndromes. First, the neoplasm must produce large amounts of bioactive substances, and their plasma levels should be elevated enough to affect target tissues. The relationship between hormone production and the development of humoral syndromes in the fifty-case study already discussed is described in Fig. 21.3. In these cases, three patients developed ectopic adrenocorticotrophic hormone (ACTH) syndrome, and two developed ectopic antidiuretic hormone (ADH: vasopressin) syndrome. Ectopic ACTH and ADH syndromes developed in patients with tumours that produced large amounts of ACTH and ADH, respectively; greater numbers of cases were found to produce the respective peptides in smaller amounts, but these were not associated with the clinical syndrome.