BACKGROUND: Pituitary adenomas display an array of hormonal and proliferative activity. Once primarily classified according to size (microadenomas, < 1 cm; macroadenomas, ≥ 1 cm), these tumors are now further classified according to immunohistochemistry and functional status. With these additional classifications in mind, the goals of the current study were to determine the prevalence of pituitary adenomas and to explore the clinical relevance of the findings.METHODS: The authors conducted a metaanalysis of all existing English‐language articles in MEDLINE. They used the search string (pituitary adenoma or pituitary tumor) and prevalence and selected relevant autopsy and imaging evaluation studies for inclusion.RESULTS: The authors found an overall estimated prevalence of pituitary adenomas of 16.7% (14.4% in autopsy studies and 22.5% in radiologic studies).CONCLUSIONS: Given the high frequency of pituitary adenomas and their potential for causing clinical pathologies, the findings of the current study suggest that early diagnosis and treatment of pituitary adenomas should have far‐reaching benefits. Cancer 2004. © 2004 American Cancer Society.

Paragangliomas are neuroendocrine neoplasms, derived from paraganglia of the sympathetic and parasympathetic nervous systems. They are most commonly identified in the head and neck, being most frequent in the carotid body, followed by jugulotympanic paraganglia, vagal nerve and ganglion nodosum, as well as laryngeal paraganglia. Abdominal sites include the well-known urinary bladder tumors that originate in the Organ of Zuckerkandl. However, other unusual sites of origin include peri-adrenal, para-aortic, inter-aortocaval, and paracaval retroperitoneal sites, as well as tumors in organs where they may not be expected in the differential diagnosis of neuroendocrine neoplasms, such as thyroid, parathyroid, pituitary, gut, pancreas, liver, mesentery, lung, heart and mediastinum. The distinction of these lesions from epithelial neuroendocrine neoplasms is critical for several reasons. Firstly, the determination of clinical and biochemical features is different from that used for epithelial neuroendocrine tumors. Secondly, the genetic implications are different, since paragangliomas/pheochromocytomas have the highest rate of germline susceptibility at almost 40%. Finally, the characterization of metastatic disease is unique in these highly syndromic lesions. In this review, we summarize updated concepts by outlining the spectrum of anatomic locations of paragangliomas, the importance of morphology in establishing the correct diagnosis, the clinical implications for management, and the impact of genetics on the distinction between multifocal primary tumors compared with malignant disease.

Medullary thyroid cancer is a rare type of neuroendocrine tumour that arises from the parafollicular cells (C cells) of the thyroid gland. It accounts for 3%–5% of thyroid cancer cases. Close to 25% of cases are familial, and 75% are considered sporadic. Familial cases are associated with a germline RET mutation; 43%–65% of sporadic cases harbour a somatic event in the gene. Germline RET mutations are associated with the autosomal-dominant inherited multiple endocrine neoplasia (MEN) 2A and 2B syndromes and the isolated familial medullary thyroid cancer syndrome. More than 100 RET codon mutations have been reported to date, with genotype–phenotype correlations that include the extent and aggressiveness of the medullary thyroid cancer and the presence of other features of the MEN2 syndromes. The latter include pheochromocytoma–paraganglioma, hyperparathyroidism, cutaneous lichen amyloidosis, and Hirschsprung disease. In this narrative review, we focus on RET proto-oncogene physiology and pathogenesis induced by germline and somatic RET mutations, the genotype–phenotype correlation, and the management and follow-up of patients with germline-mutated medullary thyroid cancer.

Ikaros transcription factors play critical functions in the control of lymphohematopoiesis and immune regulation. Family members contain multiple zinc fingers that mediate DNA binding and homooligomerization or heterooligomerization. Ikaros is abundantly expressed in pituitary mammosomatotrophs, where it deacetylates histone 3 sites on the proximal growth hormone (GH) promoter to silence gene expression. Ikaros-null mice display stunted growth with reduced circulating levels of the GH target factor insulin-like growth factor I (IGF-I). Ikaros-deficient mice have small anterior pituitary glands with a disproportionately reduced somatotroph population. Systemic administration of GH results in increased IGF-I levels and enhanced somatic growth. In contrast, reconstitution with WT lymphocytes was not sufficient to rescue the stunted growth phenotype of Ikaros-deficient mice. Ikaros was identified in mouse hypothalamic arcuate nuclei, where it colocalized with GH-releasing hormone (GHRH); in contrast, Ikaros-null mice lack GHRH immunoreactivity in the hypothalamus. Overexpression of Ikaros enhanced GHRH promoter activity and induced endogenous GHRH gene expression. These findings unmask a wider role for Ikaros in the neuroendocrine system, highlighting a critical contribution to the development of the hypothalamic–pituitary somatotrophic axis.