"In the meantime, we agree with statements issued by the major diabetes organisations that there is no need to panic" says Professor Pollak. "Insulin has an excellent risk benefit ratio and any absolute risks between the different treatments are likely to be small.

"However, careful consideration of the choices available might be wise for patients who face a high biological risk of cancer, for example those with a family or personal history of cancer. Clinicians need to be prepared to provide up-to-date advice to these people, as ongoing research continues.

"It is important to recognise that the initially surprising observation that diabetics receiving metformin treatment are substantially less likely to have cancer than expected have now been reproduced in several studies. The possibility that this off-patent drug may have uses in cancer prevention or treatment, as well as in the treatment of type 2 diabetes, is receiving serious attention from research teams of endocrinologists and oncologists."

The authors believe that future work may uncover links between insulin use and cancer risk. "Laboratory experiments have shown that some cancers respond to insulin and there are precedents where hormone therapy increases cancer risk, such as post-menopausal oestrogen replacement" says Professor Pollak.

"However, the absolute risks involved need to be characterised and placed in the context of the high absolute risks for the other more familiar morbid endpoints of diabetes. We must not lose sight of the fact that the most pressing issues facing the majority of people with diabetes, and their physicians, are those relating to glucose control and the reduction of the well-known and serious consequences of poorly controlled diabetes."

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