A new understanding of goitrogenesis: role of cytokines in the regulation of normal and aberrant thyroid growth.

Several cytokines and growth factors together with their binding proteins and/or receptors are being increasingly detected in mammalian thyroid tissue. These include epidermal growth factor, insulin-like growth factors, transforming growth factors, fibroblast growth factor, interleukins, interferons, and tumour necrosis factor-alpha. Their exact role in relation to thyroid regulation has not been fully elucidated but it is clear that many of these peptide regulatory factors are mitogenic for cultured thyrocytes. Recent evidence suggests that some thyroid cancers and benign goiters over-express receptors for a number of these growth factors. Transforming growth factor-beta is unique for its dominant anti-proliferative effect on thyrocytes concurrently exposed to potent thyroid mitogens. The mammalian thyroid cell is clearly a source as well as target of myriad polypeptide factors that probably co-regulate its normal growth and differentiation. Aberrant expression of these growth factors or their receptors might be a factor in the development of goiter.