Purpose:
Prostate Imaging Reporting and Data System (PI-RADS) 3 lesions on multiparametric magnetic resonance imaging (mpMRI) represent an equivocal category with an uncertain risk of clinically significant prostate cancer (csPCa), resulting in persistent controversy regarding biopsy indications. Our objective was to evaluate the detection rate of csPCa in patients with PI-RADS 3 only lesions undergoing robot-assisted in-bore magnetic resonance imaging (MRI)-guided prostate biopsy (RA-MRGB) and to identify clinical factors associated with cancer detection.

Material and methods:
This retrospective, single-centre study represents a predefined subgroup analysis of a previously reported institutional cohort. Men undergoing RA-MRGB between January 2021 and March 2025 were screened, and patients with a PI-RADS score of 3 on pre-biopsy mpMRI and no coexisting PI-RADS 4-5 lesions were included. Biopsy decisions were based on multidisciplinary review and shared decision-making. csPCa was defined as International Society of Urological Pathology grade group ≥ 2.

Results:
Seventeen of 84 patients with PI-RADS 3 only lesions were identified. Prostate cancer of any grade was detected in 3 patients (17.6%). csPCa was found in 2 patients (11.8%), while 14 patients (82.4%) had benign histopathology. csPCa cases demonstrated heterogeneous clinical profiles, including elevated prostate-specific antigen density or larger lesion size and prior negative biopsy. No single clinical parameter reliably excluded csPCa.

Conclusions:
When evaluated using robotic in-bore MRI-guided biopsy, PI-RADS 3 only lesions demonstrate a low but clinically relevant risk of csPCa. Biopsy decision-making in this group should rely on a multifactorial assessment rather than MRI score alone, and highly precise targeting techniques may enhance confidence in negative results.