Growth hormone, IGF-I and cancer. Less intervention to avoid cancer? More intervention to prevent cancer?

The GH/IGF-I axis has a clearly established role in somatic growth regulation and there is much evidence suggesting that it can play a contributing role in neoplastic tissue growth; a number of recent epidemiological reports indicate that it may also be an important determinant of cancer incidence. Whilst there have been previous reports of changes to the axis in patients with established cancers, these new studies are distinct in being prospective and the inferences that can be made from this are outlined in this review. The recent studies are considered within the context of other indirect epidemiological evidence, and together indicate that the GH/IGF-I axis may establish the level of predisposition to a number of common cancers and indeed that such risk may be programmed from early life. There is considerable evidence for a number of possible mechanisms, both direct and indirect, which could account for the associations between GH/IGF-I levels and cancer incidence; these mechanisms are briefly summarised. The implications of the new findings are then discussed in relation to the increasing clinical usage of chronic GH administration and the need for further studies to establish any consequent increase in cancer risk. Finally the opportunities for further work to optimise cancer risk assessment and risk reduction strategies are highlighted.