External validation of a prostate cancer nomogram on magnetic resonance/transrectal ultrasound fusion biopsy in men with prior negative systematic biopsy.

Objective To observe how the nomogram, which was created by Truong et al, works in an independent patient group by performing external validation. Patients and methods One hundred and eighty-one patients who had at least one prior negative 12-core standard systematic biopsy and lesions with PI-RADS scores of 3 or higher that were detected as a result of mpMRI were included in the study. Targeted biopsy with 12-core standard systematic biopsy was performed on all patients. Clinical and pathological features of the patients were recorded. The discrimination, calibration and decision curve analysis were performed to externally validate the nomogram. Results A total of 181 patients with previous negative 12-core systematic biopsies were analysed. One hundred and thirty-four patients (74%) had benign pathology. Radiological volume and PI-RADS scores of 4 and 5 were found as independent predictors of benign pathology. The area under the curve (CI 95%) was found to be 0.80 (0.73-0.87), indicating good discrimination. The median residual was calculated as -0.0873, the intercept as -0.0690, the slope as 0.8927 and r2 as 0.2586, indicating good calibration. The standardised net benefit of follow-up decisions was found to be 0.54 and 0.36 at the probability threshold of 0.7 and 0.8, respectively. Conclusion The original model showed good discrimination and calibration with our data. Defining a high probability threshold for clinical use would be appropriate for centres with high benign biopsy rates similar to our centre.