The role of adc ratios measured on multiparametric MRI in the diagnosis of clinically significant prostate cancer and their correlation with Gleason scores

Objective: The aim of this study was to investigate the diagnostic value of apparent diffusion coefficient (ADC) values and ADC ratios obtained from prostate multiparametric MRI (mpMRI) in distinguishing clinically significant prostate cancer (csPKa), and to evaluate the relationship of these parameters with Gleason scores. Materials and Methods: A total of 188 patients who underwent pre-biopsy prostate mpMRI between January 2021 and January 2025 were retrospectively analyzed. Sixty-two patients with pathologically confirmed malignancy (GS ≥6) were classified as the malignant group, while 126 patients diagnosed with benign features or normal tissue were classified as the benign group. Clinical parameters such as age, PSA, prostate volume (PV), and PSA density (PSAD), along with ADC values measured from lesion sites and contralateral normal zones, were recorded. In the malignant group, the ADC ratio was calculated using the tumor region ADC (ADC-ML) and the contralateral normal zone ADC (ADC-MN) at the same level. In the benign group, the ADC of the suspicious area (ADC-BL) was compared to that of the contralateral normal tissue (ADC-BN). The collected data were statistically analyzed. Results: The mean ADC values of malignant lesions were significantly lower than those of benign tissues (p<0.001). According to ROC analysis, the optimal cut-off value for ADC was determined to be 994 ×10⁻⁶ s/mm², yielding a sensitivity of 96.8% and specificity of 94.0% (AUC=0.994). For the ADC ratio, the best threshold was 0.57, with both sensitivity and specificity calculated at 95.2% (AUC=0.985). A significant negative correlation was found between Gleason scores and both ADC values and ADC ratios (p<0.001). Additionally, decreased ADC values in contralateral normal tissue in patients with Gleason score ≥7 suggest the presence of a "field cancerization" phenomenon that may influence ADC ratios. Conclusion: ADC values and ratios derived from prostate mpMRI are reliable and reproducible biomarkers in the diagnosis and assessment of prostate cancer aggressiveness. This study highlights the potential clinical utility of ADC ratios, which are not directly defined in the PI-RADS v2.1 system, and recommends their integration into diagnostic workflows in future large-scale, multicenter studies.