Re-evaluating the biological significance of seminal vesicle invasion (SVI) in locally advanced prostate cancer.

Objective: • To examine the impact of seminal vesicle invasion (SVI) in patients with locally advanced (pT3) prostate cancer on clinical outcome. • To explore the clinical association of SVI with metastatic disease. • To distinguish between the possibilities that either seminal vesicles possess their own biological significance and represent a privileged staging site for systemic tumour cell dissemination, or that their invasion is a surrogate marker for an aggressive large-volume poorly differentiated cancer.

Patients And Methods: • Patients with extraprostatic extension (EPE) and/or SVI were identified from a prospectively recorded and maintained prostate cancer database. • Patients were categorised according to the presence of SVI as determined by routine pathological assessment. Tumour volumes were measured routinely by computed planimetry at the time of histological assessment. • The impact of SVI on biochemical recurrence with a definition of a prostate-specific antigen (PSA) level of ≥0.2 ng/mL, as well as a clinically significant recurrence defined as failure with a PSA doubling time of <6 months, was determined by univariable and multivariable Cox regression analysis.

Results: • Of 249 patients with pT3 disease, 46 (18%) had SVI, 40 (87%) by direct extension and six (13%) metastatic. • Tumours with SVI had significantly greater tumour burden as determined by total tumour volume (7.2 vs 3.7 mL, P < 0.001), index tumour volume (6.8 vs. 3.4 mL, P < 0.001) and percentage tumour volume (21.8 vs 12.4 %, P= 0.001). • After controlling for tumour volume and Gleason score, the presence of SVI did not significantly predict for the development of a significant PSA recurrence.

Conclusions: • Our results suggest that SVI is a surrogate marker of larger and more aggressive tumours with higher Gleason scores rather than a privileged site of tumour cell dissemination.