'Big ACTH' and calcitonin in an ectopic hormone secreting tumour of the liver.

A young man presented with rapidly developing Cushing's syndrome which was due to the ectopic secretion of ACTH and beta-MSH-like material from hepatic tumour deposits, possibly originating from biliary radicals. This association of the ectopic ACTH syndrome has not previously been described. During the 22 month course of the illness the plasma immunoreactive ACTH and 'beta-MSH' concentrations rose by logarithmic progression. The plasma calcitonin concentration was also raised but did not change during the last 12 months. At any stage of the illness the plasma concentration of the ecotopically produced hormones was stable except that after hydrocortisone there were inconstant variations. During the course of the illness the ectopic ACTH became biologically less potent. This ineffectural ACTH was present in the plasma, in the tumour, and in the medium in which the tumour was cultured, in a large molecular weight form. This 'big ACTH' differed from the normal ACTH found in the patient's pituitary and from authentic ACTH in its immunochemical character: the C-terminal antigenic determinant (33-39 region of ACTH) was masked in the large molecular weight form but was uncovered after extraction in neutral buffer and this 'big ACTH' was more readily extracted from the tumour at pH 7.0. The tumour tissue also contained immunoreactive beta-MSH-like material and immunoreactive calcitonin which resembled calcitonin M chromatographically.