Molecular adrenocortical tumourigenesis

Adrenocortical neoplasms are the most frequent abnormality of the adrenal cortex. Most of these lesions are clinically silent and are detected incidentally by ultrasound or computed tomography. The prevalence of these so-called 'incidentalomas' in the general population is around 1%, increasing with age and reaching 6% among those in the age range 60-70 years. In contrast, primary adrenocortical carcinoma, a highly malignant tumour, is rare, having an incidence of one case per million per year. Recent progress has been achieved in the understanding of adrenocortical tumourigenesis by mapping and identification of genes responsible for hereditary tumours that involve the adrenal gland. Investigation of the clonal composition of adrenal tumours demonstrates that adrenal carcinomas are monoclonal, whereas adrenal adenoma may be polyclonal in approximately 25-40% of cases. Oncogenes and tumour-suppressor genes involved in adrenal carcinomas include mutations in the p53 tumour-suppressor gene and rearrangements of the chromosomal locus 11p15.5 associated with IGF II hyperexpression. Constitutive activation of the ACTH receptor-G protein-cAMP signal cascade does not play a role in adrenal tumour formation. Conversely, deletions of the ACTH receptor gene have recently been found in undifferentiated adenomas and in aggressive adrenocortical carcinomas, and, more recently, confirmed in a larger series of tumours. The available literature indicates that the signalling pathways of adrenocortical tumours are different from those of other endocrine neoplasms, such as pituitary and thyroid adenomas.