Topography of Lymph Node Metastases in Prostate Cancer Patients Undergoing Radical Prostatectomy and Extended Lymphadenectomy: Results of a Combined Molecular and Histopathologic Mapping Study

To determine the anatomic extent of pelvic lymph node dissection (PLND) in prostate cancer (PCa) patients at the time of radical prostatectomy (RP), knowledge about the topography of lymph node (LN) metastases is required. Because small-volume LN metastases may be missed by standard histopathologic examination, we performed an anatomic mapping study combining molecular and histopathologic LN examination in PCa patients treated with RP and extended PLND (ePLND). A total of 52 patients with intermediate- (n = 15) and high-risk (n = 37) PCa underwent RP and ePLND without neoadjuvant treatment. ePLND included dissection of the obturator fossa and the external, internal, and common iliac vessels. LNs ≥3 mm in diameter were analysed by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) for prostate-specific antigen (PSA) expression and by standard histopathology. Topography of positive LNs was determined descriptively. Of 1469 dissected LNs (median: 27 LNs per patient), 1186 LNs were ≥3 mm. Molecular LN analysis was positive in 127 LNs of 27 patients (52%) including 32 LNs of 12 patients (23%) with histopathologic positive LNs. Molecular examination was negative in 3 of 35 histopathologic positive LNs (9%). Combining both molecular and histopathologic findings, positive LNs were located in the standard PLND field defined by obturator fossa and external iliac vessels in 71%, along the internal iliac vessels in 16%, and along the common iliac vessels in 13%. Of LN-positive patients, 63% had LN metastases outside the standard PLND field. The internal iliac field was involved in 48% and the common iliac field in 37% of node-positive patients. Notably, internal and common iliac vessels were the only positive regions in 7% and 11% of node-positive patients, respectively. A limitation is the small number of patients included. These findings underline the enhanced sensitivity of qRT-PCR in comparison with standard histopathology for detection of small-volume LN metastases in PCa patients. Our results support an ePLND including the common iliac vessels, at least up to the ureteral crossing, to optimise nodal staging and to remove LNs potentially harbouring metastases.