Infrequent elevation of plasma ACTH in patients with bronchogenic carcinoma

Older methods for radioimmunoassay of ACTH in human plasma have detected a high frequency of plasma ACTH elevation in patients with lung cancer, even in the absence of Cushing's syndrome. It now appears evident that these assay systems measure biologically inactive forms and fragments of ACTH. Since ectopic Cushing's syndrome may be clinically atypical, a radioimmunoassay for ACTH that correlates with the clinical state would be of value. Accordingly, circulating plasma corticotropin (ACTH) levels were measured in 39 consecutive patients with biopsy-proven, untreated lung cancer, all without evidence of Cushing's syndrome. In only one instance was ACTH found to be elevated by the method of assay used. Two interpretations are justified: (1) elevated plasma ACTH levels are infrequent in patients with lung cancer, or (2) ACTH measurements vary according to the assay system used.