The aim of this study was to evaluate the difference in malignancy incidence by evaluating time-dependent HbA1c levels among diabetic patients in a longitudinal study.
We conducted a retrospective longitudinal study at large academic hospital, Tokyo, Japan, from 2006 to 2016. We included all diabetic patients who were 50 years or older and who underwent health check-ups at the Center for Preventive Medicine. Those patients with a prior history of malignancies were excluded. We categorized patients into five groups on the basis of HbA1c measurements: <5.4, 5.5–6.4, 6.5–7.4, 7.5–8.5, >8.5%. Our primary outcome was the development of any types of malignancy. Longitudinal analyses by a mixed effect model with time-dependent HbA1c levels were applied in order to take into account fluctuations in HbA1c levels within the same patient.
In total, 2729 participants were included in this study, where the mean age was 62.6 (standard deviation (s.d.): 7.8) and 2031 (74.4%) were male. The mean disease duration of diabetes was 7.6 (s.d.: 7.6) years, and 1688 (61.8%) were prescribed medications. Median follow-up was 1443.5 (interquartile range (IQR): 2508) days and 376 (13.8%) developed malignancies. Compared to the reference range of HbA1c (5.5–6.4%), the odds ratios for developing malignancies among the other HbA1c level groups were similar and not statistically different (OR: 0.98, 95% CI:0.31–3.15 (for HbA1c <5.4%); OR: 0.88, 95% CI: 0.69–1.12 (for HbA1c 6.5–7.4%); OR: 0.88, 95% CI: 0.64–1.22 (for HbA1c 7.5–8.4%); OR 1.07, 95% CI: 0.70–1.66 (for HbA1c >8.5%)).
In our study, there was no association between glycemic control and the development of future malignancies. Compared to very strictly controlled HbA1c levels, both excessive control and good or bad control had a statistically similar risk of developing malignancies.