Prostate cancer mortality is higher for overweight men with high insulin secretion prior to diagnosis

Researchers from Brigham and Women’s Hospital (BWH) and colleagues found that excess bodyweight and high plasma concentrations of C-peptide (a protein that reflects the amount of insulin secretion) in men who are subsequently diagnosed with prostate cancer are reliable indicators that they are more likely to die from their disease than those with lower levels. This substudy of the Physician’s Health Study is found in an article published online 5 October, and in the November edition of Lancet Oncology.

Jing Ma, MD, MPH, PhD, of the Department of Epidemiology at BWH, and colleagues assessed data from 2546 men diagnosed with prostate cancer during 24 years of follow-up in the Physician’s Health Study. The association between baseline BMI, baseline plasma C-peptide concentrations, and BMI measured at 8-years of follow-up and subsequent prostate cancer-related death was examined.

Several past studies have suggested that men who are overweight, as measured by body mass index (BMI), have an increased risk of prostate cancer progression and disease-related death. However, long-term, prospective data on prostate cancer-specific mortality have been scarce. Furthermore, although the high insulin concentrations associated with obesity could potentially explain the adverse effect of obesity on prostate cancer mortality, no studies had assessed the association between pre-diagnostic plasma concentrations of C-peptide and prostate cancer-specific mortality.

Using the Physician’s Health Study, researchers found that men who were overweight (BMI = 25–29.9 kg/m²) or obese (BMI > 30 kg/m²) before diagnosis were significantly more likely to die from their prostate cancer than men of normal weight (BMI < 25 kg/m²). This trend remained significant after controlling for clinical stage and Gleason grade. Baseline C-peptide concentrations were available for 827 men and those with the highest C-peptide plasma concentrations also had a higher risk of prostate cancer mortality compared with men with the lowest concentrations. Men with both a high C-peptide concentration and high BMI prior to diagnosis of prostate cancer had a four times higher risk of disease-specific mortality, independent of other clinical predictors.

The findings provide “further impetus for men to avoid becoming overweight and to decrease their risk of metabolic syndrome by physical activity and diet; and also adds to the rationale for investigation of new therapeutics and prevention strategies, such as use of insulin-lowering or anti-diabetic drugs,” says Dr Ma.

Researchers also note that measurement of a blood hormone level, even prior to the diagnosis of a cancer, allows one to predict the behaviour of cancer that might arise many years in the future.

(Source: Lancet Oncology: Brigham and Women’s Hospital: October 2008)