The immediate cause of the hypoglycaemia (Fig. 20.21) is overproduction by the tumour of either normal or a slightly altered form of IGF2, except in a tiny proportion of lymphomas in which auto-antibodies to the insulin receptor appear to be involved. IGF2 that gains access to the plasma is normally avidly bound by the various specific IGF-binding proteins that are present in the circulation. Ordinarily, therefore, IGF2 in the circulation does not produce hypoglycaemia.
The most important IGF-binding protein is IGF-BP3, which is produced in the liver under the influence of growth hormone.
