Peripheral lung carcinoid tumor producing predominantly gastrin‐releasing peptide (GRP) morphologic and hormonal studies

: A carcinoid tumor of the peripheral lung producing gastrin-releasing peptide (GRP), a peptide hormone known to be present in the endocrine cells of fetal bronchial epithelium, is reported. Brain-gut peptide hormones in this tumor were assayed by radioimmunoassays, localized by immunohistochemistry and characterized by gel filtration. Electron microscopic study revealed that tumor cells resembled P-cells of normal human fetal bronchial epithelium. While GRP-containing cells were predominant in this tumor, calcitonin-containing cells were also found in some areas. Difference in distribution of hormones according to histologic features was noted in the tumor. A greater portion of the tumor showed spindled cells that predominantly contained GRP, and a smaller portion of the tumor showed cells arranged in tubular or trabecular patterns that mainly contained calcitonin. The gel-filtration pattern of the tumor extracts consisted of two peaks, one of these corresponded to the synthetic replicate of porcine GRP, and another was considered to correspond to C-terminal fragments of the peptide.