Up to now, the studies involving
diabetes mellitus and
malignancies show controversial results: Many of them have found incidences of
malignancies that were comparable or even lower than those in nondiabetic subjects; others conclude that
diabetes mellitus is linked to a higher incidence of
malignancies and/or a predictor of mortality from
cancer.
Insulin and its precursors, pro- and pre-
proinsulin, have been shown to have some homology to the
insulin-like growth factors, but, moreover they have some affinity to bind at receptors of the
tumor growth factor and some hybrids too. Hence, an association between
diabetes mellitus,
insulin, hyperinsulinaemia, and
carcinogenesis appears plausible. On the other hand,
diabetes mellitus can influence different
hormone levels. In some
tumor entities, such as prostate
carcinoma, this effect can somewhat counterbalance the direct mitogene effect of
insulin and its precursors. All in all, as a result of the complexity of these mechanisms and the differences between the
tumor entities, the question whether
diabetes mellitus is associated with an increased or a reduced risk for the development and in respect of the prognosis of
cancer cannot be answered. The only way to give some answer is to focus on specific
tumor entities: It seems that
diabetes mellitus and/or hyperglycaemia are independent risk factors and/or predictors at least in respect of
cancer of the colon, pancreas, female breast, endometrium, and, in men, of the liver and bladder. However, most of these data were assessed in patients with
type 2 diabetes mellitus. This makes it highly questionable whether the data can easily be transferred to patients with
type 1 diabetes. Moreover, additional potential limitations are that most of the studies do not focus on the treatment modality or the race of participants. In conclusion, up to the present, we have an increased risk for some and a reduced risk for other
tumor entities, but still, we cannot give the general answer.