Statistical Analysis
The combined effect of melatonin and cortisol levels on prostate cancer could be measured at the same time to calculate the urinary melatonin-sulfate/cortisol (M/C) ratio by dividing urinary melatonin-sulfate levels by urinary cortisol levels. Differences between the patient and control groups in urinary biomarkers such as cortisol, melatonin-sulfate, and the M/C ratio were studied using the Wilcoxon Rank-Sum Test. Furthermore, we dichotomized these urinary markers with medians of 23.92 ng/mg creatinine for cortisol, 1.81 for the M/C ratio, and 42.83 ng/mg creatinine for melatonin. 95% confidence intervals (CIs) and odds ratios (OR) were estimated using the unconditional logistic regression models for the correlation between urinary markers and risk of prostate cancer. Family history of prostate cancer, habits (smoking, alcohol), age at the time of the study (<65 vs. ≥ 65 years), PSA level (<10 vs.> 10 ng/mL) were considered for all analyses.
The cases were also categorized as advanced (end-stage) cancer (extraprostatic stage T3a or higher, N1/M1) and localized prostate cancer (stage T2 or T1) 20. The risks of developing advanced (end-stage) and localized prostate cancer based on the control group were determined using the multi-category logistic regression models. Polytomous logistic models containing categorical variables and their cross-products were fitted to appraise multiplicative interaction. The significance of multiplicative interaction was evaluated for each pair of comparison using the Wald Z-tests for cross-product terms. All two-sided p-values were considered significant if < 0.05.