Aspects of Lymph Node Staging in Intermediate- and High-Risk Prostate Cancer

The aim of this thesis was to explore the role of pelvic lymph node dissection (PLND) in staging newly diagnosed prostate cancer patients and to evaluate its long-term impact on oncological outcomes. Surgical removal of pelvic lymph nodes with subsequent microscopic evaluation is the most reliable method for detecting nodal involvement, but the procedure is invasive and associated with morbidity. Consequently, different imaging modalities are generally preferred to guide treatment decisions. However, their diagnostic accuracy should be validated against that of extended PLND (ePLND) as the reference standard. The thesis is based on four papers. The first three studies evaluated different imaging approaches for the detection of nodal spread in intermediate and high-risk prostate cancer. In Paper I, conventional magnetic resonance imaging (MRI) with only T1- and T2-weighted (nonfunctional) sequences was evaluated. Although this protocol is widely applied prior to prostate biopsy, it demonstrated the lowest pooled sensitivity of 24.5%, and even patients with high-volume nodal metastases were missed. In Paper II, the addition of diffusion-weighted imaging (DWI) improved MRI diagnostic performance, achieving a sensitivity of 55%. Paper III evaluated [11C]-acetate positron emission tomography/computed tomography, which also showed limited sensitivity at 38%. However, in papers II and III, the missed cases predominantly represented low-volume nodal disease. Paper IV investigated the long-term oncological impact of ePLND in high-risk settings before prostate external beam radiation therapy (EBRT), using limited PLND as the reference group. ePLND was associated with improved biochemical recurrence-free, metastasis-free, and cancer-specific survival with differences mostly evident 10–15 years after EBRT. Collectively, the current imaging modalities examined in this thesis perform poorly and cannot replace ePLND, which appears to improve long-term oncological outcomes.