Clinicopathological analysis of the absence of seminal vesicle invasion in prostate cancer patients without radiological evidence on magnetic resonance imaging.

Background: In definitive radiotherapy for localized prostate cancer, the seminal vesicle is included in the target volume for intermediate- and high-risk cases, though this increases the risk of toxicity to the bowel and rectum. This study retrospectively examined clinicopathological data to assess the absence of seminal vesicle invasion (SVI) in prostate cancer patients without radiological evidence of SVI using preoperative magnetic resonance imaging (MRI). Materials and methods: Patients with cT1c-cT3a prostate cancer who underwent radical prostatectomy between March 2010 and February 2024 were retrospectively selected, excluding those with distant metastasis, missing MRI data, preoperative systemic therapy, or delayed surgery post-biopsy. Preoperative risk factors [age, initial prostate-specific antigen (PSA), grade group (GG), clinical T stage, positive core ratio] and postoperative pathology were analyzed to assess SVI risk. The impact of GG changes between biopsy and postoperative pathology on risk classification and SVI treatment intensity in radiotherapy was also examined. Results: Of 368 patients, 308 met the inclusion criteria. SVI was observed in 26 patients (8.4%). Significant predictors of SVI included GG, initial PSA ≥ 8.6, and positive core ratio, with a positive core ratio < 0.5 and GG ≤ 3 indicating an SVI risk under 10%. GG discrepancies between biopsy and surgery were noted in 182 cases (59.1%), but had minimal impact on risk classification and SVI risk. Conclusions: Patients with a positive core ratio <0.5 had a low risk of SVI. GG discrepancies did not significantly underestimate prostate cancer risk, minimizing the risk of failing to treat true SVI.