Ectopic hormone production.

Current understanding of the phenomenon of ectopic hormone production is largely based on a histopathological and immunocytochemical analysis of peptide hormone secreting tumours arising in non-endocrine tissues. Recent advances in the study of gene regulation show that the tissue-specific expression of genes is a highly sophisticated process and is unlikely to be disturbed by a spontaneous event such as point mutation in DNA. Study of several genes for frequently found ectopic hormones, i.e. prop-opiomelanocortin, vasopressin/neurophysin II, gastrin-releasing peptide, parathyroid hormone-related peptide, calcitonin gene-related peptide and beta-chorionic gonadotropin, suggests they are transcribed as they would be in their natural cell of origin. It is argued therefore that these data are compatible with the concept that the tumour cell of origin was capable of expressing these peptides, if only in a minor or transient manner. In one example, the ectopic ACTH syndrome, it is also necessary to explain the non-suppression of this gene's expression by elevated levels of glucocorticoids. Recent work suggests that this may result from physically present, but biologically inactive glucocorticoid receptors, a phenomenon that has occasionally been noted in hormonally inactive tumour tissue and cell lines.