2.6. Statistical Analysis

All of the determined blood-based biomarkers or metabolites were normalized. The values obtained at the first visits were defined as 100%. The relative secretion values are shown in box plots with medians and interquartile ranges (IQRs). Whiskers represent the minimum and maximum values. Furthermore, all of the data were tested for normal distribution using the Shapiro−Wilk test, and the parameters are presented as the median ± range.

Finally, for the identification of possible correlations between the different markers for the different study groups, Spearman’s rank correlation coefficient (r_s) was determined and is represented in a heatmap. The reported p-values are two-sided, and ≤0.05 was considered significant. The accuracy of the selected biomarker levels was evaluated by receiver operating characteristic (ROC) analysis. For this analysis, we used no cut-offs, but the median was six visits performed for 24 months survival. The optimal cut-off for the Kaplan−Meier analysis of PSA based on the ROC curve was calculated by the largest value of the formula, sensitivity + specificity − 1, from the median PSA level for every mCRPC patient (likelihood ratio). The mean CTC count was determined based on the CTC counts of visits 1–8 (V1–V8). Kaplan−Meier analysis was used to analyze the overall survival (OS) depending on the mean CTC count. The survival estimates in different groups were compared using the log-rank (Mantel−Cox) test. All of the statistical analyses were performed using GraphPad Prism software versions 7 and 9.