Seminal vesicle invasion (SVI) is a high-risk factor for prostate cancer. SVI is observed in various patterns, yet no standardized method exists for evaluating its extent. Therefore, we analyzed the clinical characteristics of pT3b prostate cancer and conducted a refined histopathologic analysis of seminal vesicle (SV) specimens to closely examine the extent and pattern of SVI and assess its clinical implications.

A single surgeon’s database on robotic radical prostatectomy from July 2020 to December 2024 was retrospectively reviewed, identifying 73 patients staged as pT3b. Preoperative clinicopathological data and image review was performed. A refined histopathologic analysis was conducted to assess the presence of SV stromal invasion, peri-SV soft tissue involvement, and the surgical margin status of peri-SV soft tissue. The number of harvested and positive lymph nodes (LN) was also examined.

Among the 73 patients, 35 (47.9%) were clinically staged as cT3b, while the remaining 38 patients were preoperatively diagnosed as cT3a or lower. Prostatectomy specimens revealed bilateral SVI in 33 patients (45.2%). Notably, peri-SV soft tissue invasion was observed in 54 patients (74.0%), among whom clear surgical margins were secured in 49 (90.7%), while 5 (9.3%) had positive margins. Vas deferens invasion was present in 25 patients (34.2%). After excluding 7 patients who had received preoperative antiandrogen therapy and 8 who had not undergone pelvic lymph node dissection (PLND), 58 patients remained for analysis of PLND. The mean number of harvested LNs was 15.46 (3 – 34), and the mean number of involved LNs were 1.06 (0 – 16). Among the 58 patients, 25 (43.1%) had LN metastasis. Gleason grade group 4 or 5, peri-SV soft tissue invasion, vas deferens invasion and lymphovascular invasion were significantly associated with pelvic LN metastasis (p = 0.011, 0.043, p = 0.024, and p < 0.001, respectively).

In pT3b patients, the high rate of peri-SV soft tissue involvement highlight the thorough completeness of tumor removal, including meticulous resection of peri-SV soft tissue.