This paper has reviewed current knowledge of clinical, biochemical, and morphological manifestations of extracranial GRH-producing tumors. Excessive GRH release stimulates pituitary somatotrophs causing elevation of blood GH levels and acromegaly. In some patients with GRH-containing tumor, blood GH concentrations are normal and no acromegaly develops. GRH-producing tumors associated with acromegaly are rare. Based on a critical analysis of the literature, 30 tumors are accepted as definitive. They possess unique features: occurrence in young age, female preponderance, foregut derivation, benign biological behavior, small secretory granules, and frequent association with MEN type I syndrome. The pancreas and lung are common primary sites. GRH-containing tumors unassociated with acromegaly include those of gut and thymus, small cell carcinoma of lung, and medullary carcinoma of thyroid. Several tumors are plurihormonal. In contrast to somatotroph adenoma seen in patients with classical acromegaly, the hypophysial lesion represents somatotroph hyperplasia in acromegalic patients with GRH-producing tumor. This finding indicates that GRH not only increases somatotroph secretory activity but causes somatotroph proliferation. Studies of GRH-producing tumors are of fundamental importance in obtaining a deeper insight into endocrine activity of pituitary somatotrophs and the pathogenesis of GH-secreting pituitary adenomas associated with acromegaly; the importance of GRH in the etiology of acromegaly is still unresolved. The relationship between GRH-secreting tumors and MEN type I syndrome is controversial; further studies are required to elucidate whether they represent two distinct entities or whether GRH-producing tumors accompanied by acromegaly are only forme fruste manifestations of MEN type I syndrome.

Growth Hormone-Releasing Hormone-Producing Tumors: Clinical, Biochemical, and Morphological Manifestations*

THE clinical features of acromegaly result directly or indirectly from sustained hypersecretion of growth hormone.1 2 3 Somatotroph-cell adenomas, or in rare cases hyperplasia, constitute the pathologic pituitary lesions causing acromegaly.4 , 5 Also in rare cases, acromegaly may be caused by ectopic somatotroph-cell adenomas in the sphenoid or parapharyngeal sinuses.4 , 5 Attention has recently been focused on the elaboration of growth hormone–releasing factors by carcinoid6 and pancreatic islet-cell tumors7 causing acromegaly. The structure of human growth hormone–releasing factor was, in fact, first elucidated from two such pancreatic tumor extracts, which were shown to stimulate growth hormone release both in vitro and in vivo.8 , 9 Ectopic . . .

Acromegaly Due to Secretion of Growth Hormone by an Ectopic Pancreatic Islet-Cell Tumor

Pathology of pituitary tumors.

Publisher Summary This chapter reviews the physiological and clinical studies of growth hormone (GH) and growth hormone releasing factor (GRF). GRF is the last of the classical hypothalamic hormones isolated. The isolation of GRF was only possible by the identification of peripheral GRF-secreting tumors. A major problem in isolating GRF was the minute amount of peptide presents in the hypothalamus, which, in addition, contained high concentrations of the GH release-inhibiting hormone, somatostatin. Its application to animal and human studies has opened a new horizon in GH physiology and pathophysiology. The pulsatile pattern of GH secretion in several mammalian species is accounted for by a dynamic interaction of hypothalamic somatostatin and GRF at the somatotroph. The increased GH secretion of the male rat is accounted for at least in part by increased percentage of somatotrophs, increased GH secretion per cell, and increased sensitivity to GRF. Studies with GRF in GH-deficient subjects have demonstrated that the majority of these patients do not suffer from a pituitary defect, but instead from a hypothalamic neurosecretory defect giving rise to GRF deficiency. Preliminary data demonstrate that GRF accelerates growth in GH-deficient children. GRF offers the prospect of restoring endogenous GH secretion to children and adults with GH deficiency. In addition, it appears that to restore pulsatile GH secretion GRF may be administered either in a pulsatile or continuous fashion. The tight regulation of GH by nutritional factors and the known metabolic effects of GH suggest that it is an important regulator of metabolism.

Physiological and clinical studies of GRF and GH.

A comparative immunocytochemical investigation was performed on a series of 59 pancreatic endocrine tumours using a panel of seven markers for neuroendocrine neoplasms: neurone specific enolase (NSE), PGP 9.5, chromogranin A (CgA), PHE5, prealbumin (Pa), HISL-19, and alpha-subunit of human chorionic gonadotropin (α-HCG). Most markers can be separated into two groups characterized by an identical immunoreactive cellular compartment and substantial overlapping in the immunohistochemical results. The first group comprises soluble cytoplasmic proteins such as NSE and PGP 9.5 and is characterized by a diffuse, homogeneous staining of the cell cytoplasm that is not related to the type of hormone produced or the degree of cell differentiation. The second group includes antigens located in the cell secretory granules such as CgA, PHE5, Pa and HISL-19 and is characterized by a heterogenous, often polarized cell staining. The latter markers strongly react with benign glucagonomas and PP-omas and, in contrast with those of the former group, are stricly neuroendocrine-specific. However, they often are less effective in staining insulinomas and malignant tumours. An additional, distinctive and useful characteristic of the HISL-19 antibody was its ability to label the Golgi complex also in tumours with absent granular staining. Finally, α-HCG was found in 9 of 16 malignant tumours (mostly glucagonomas and insulinomas) and in 4 of 43 benign neoplasms (all insulinomas). The latter finding is not in accordance with the reputed specificity of the α-HCG expression by pancreatic endocrine tumours as a marker for tumour malignancy.

Comparative study of seven neuroendocrine markers in pancreatic endocrine tumours.

Somatoliberinoma: morphologic characteristics

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Somatoliberinoma: morphologic characteristics