Investigating the prostate specific antigen, body mass index and age relationship: is an age–BMI-adjusted PSA model clinically useful?

Purpose: Previous studies indicate a possible inverse relationship between prostate-specific antigen (PSA) and body mass index (BMI), and a positive relationship between PSA and age. We investigated the associations between age, BMI, PSA and screen-detected prostate cancer to determine if an age-BMI adjusted PSA model would be clinically useful for detecting prostate cancer.

Methods: Cross sectional analysis nested within the UK ProtecT trial of treatments for localised cancer. Of 18,238 men aged 50-69 years, 9,457 men without screen-detected prostate cancer (controls) and 1,836 men with prostate cancer (cases) met inclusion criteria: no history of prostate cancer or diabetes; PSA <10 ng/ml; BMI between 15 and 50 kg/m2. Multivariable linear regression models were used to investigate the relationship between log-PSA, age and BMI in all men, controlling for prostate cancer status.

Results: In the 11,293 included men, the median PSA was 1.2 ng/ml (IQR: 0.7 to 2.6); mean age 61.7 years (SD: 4.9); and mean BMI 26.8 kg/m2 (SD: 3.7). There was a 5.1% decrease in PSA per 5 kg/m2 increase in BMI (95% CI: 3.4% to 6.8%) and a 13.6% increase in PSA per 5 year increase in age (95% CI: 12.0% to 15.1%). Interaction tests showed no evidence for different associations between age, BMI and PSA in men above and below 3.0 ng/ml (all p for interaction > 0.2). The age-BMI adjusted PSA model performed as well as an age-adjusted model based on National Institute for Health and Care Excellence (NICE) guidelines at detecting prostate cancer.

Conclusion: Age and BMI were associated with small changes in PSA. An age-BMI adjusted PSA model is no more clinically useful for detecting prostate cancer than current NICE guidelines. Future studies looking at the effect of different variables on PSA, independent of their effect on prostate cancer, may improve the discrimination of PSA for prostate cancer.