Why do men with DM have lower reported rates of prostate cancer?

Takeaway

• Findings do not support the hypothesis that the inverse association between diabetes mellitus (DM) and prostate cancer risk is mediated through use of glucose-lowering medications that lower PSA and mask prostate cancer presence.
• Rather, they suggest detection bias, e.g., fewer biopsies undertaken when PSA is elevated.

Why this matters

• Reasons for reported lower prostate cancer incidence among men with diabetes unclear.

Study design

• Stockholm PSA and Biopsy Register data analysed for men aged 40-79 years who used metformin (n=4583), sulfonylurea (1104), insulin (987), and first of any glucose-lowering medication (4424).
• Funding: Swedish Cancer Society, Swedish Research Council, Swedish Research Council for Working Life.

Key results

• In multivariate analysis, PSA testing rates were slightly higher among men prescribed metformin (relative rate ratio, 1.07; 95% CI, 1.06-1.09) and sulfonylurea (1.06; 1.03-1.08), but lower for insulin (0.79; 0.77-0.81).
• Among men with PSA level ≥3.0 ng/mL, vs no prior exposure, aORs (95% CIs) for receiving a biopsy were:
  • 0.87 (0.80-0.96) for metformin users,
  • 0.88 (0.78-1.00) for sulfonylurea use, and
  • 0.83 (0.74-0.93) for insulin use.
• Drug exposure was not associated with biopsy findings, regardless of biopsy trigger.

Limitations

• Not all glucose-lowering medications considered.
• Prescription data prior to July 2005 unavailable.
• Data lacking on potential confounders.