Conditions Necessary for Clinical Syndromes (3)	

It is well established that overproduction of calcitonin is not associated with any humoral syndrome, because calcitonin has no clinically detectable biological activity. However, overproduction of GRP or GHRH from neuroendocrine tumours has been reported to induce Cushing's syndrome or acromegaly, respectively. These syndromes were not observed in the patients with small-cell lung carcinoma; therefore it is reasonable to speculate that the biological activities of these peptide hormones are rather weak, and that the amount of peptide hormone that was produced by each small-cell lung neoplasm was not great enough to develop humoral syndromes. 
These features are not limited to small-cell lung carcinoma or to ectopic hormone production, but are common to a variety of carcinoma that produce bioactive substances.