Insulin analogues and cancer risk: the emergence of second-generation studies.

A number of observational studies have linked insulin glargine (A21Gly,B31Arg,B32Arg human insulin) with a putative increased cancer risk, particularly breast cancer, but many of these 'first generation' studies had study design and analysis flaws, and were inconclusive. A small number of 'second generation' studies are now emerging in which the applied pharmaco-epidemiological principles are more robust. For example, when Ruitar and colleagues (Diabetologia DOI: 10.1007/s00125-011-2312-4 ) focused specifically on breast cancer rather than all incident cancer risk, they were able to show a positive association with insulin glargine for breast cancer although there was no association with all incident cancer risk. A list of preferred qualities for pharmaco-epidemiological studies is presented.