Lymph node count impacts survival following post-chemotherapy retroperitoneal lymphadenectomy for non-seminomatous testicular cancer: a population-based analysis

Objective: To evaluate the prognostic significance of lymph node count (LNC) at post-chemotherapy retroperitoneal lymphadenectomy (PC-RPLND) in metastatic non-seminomatous germ cell tumour (NSGCT) using the Surveillance, Epidemiology, and End Results (SEER) database and National Cancer Database (NCDB). Patients and methods: SEER (2000–2013, n = 572) and NCDB (2004–2013, n = 731) identified patients undergoing PC-RPLND for Stage II and III NSGCT. Correlation between linear or categorial variables and LNC was conducted using Spearman's rank correlation or Kruskal–Wallis test by ranks. Patients were stratified by ≤20, 21–40, and >40 LNs for Kaplan–Meier analysis. Cox proportional hazards models evaluated the association of LNC at PC-RPLND with overall mortality (OM) in the NCDB and cancer-specific mortality (CSM) in the SEER database. The relationship between LNC and OM or CSM was also modelled as a non-linear function to determine a threshold for survival benefit. Results: Amongst all patients, the median (interquartile range) LNC was 17 (3–26) LNs in the NCDB, and 18 (6–31) LNs in the SEER database. More recent diagnosis year, higher hospital volume, higher median income, private insurance status, and positive LNC were associated with greater total LNC in one or both databases (P < 0.05). On Kaplan–Meier analysis, >40 LNs was associated with 5-year cancer-specific survival (CSS) of 99% and overall survival (OS) of 96%, whereas ≤20 LNs had a 5-year CSS of 91% and OS of 78% (CSS, P = 0.04; OS, P < 0.01). Risk-adjusted Cox model showed increasing LNC (per node) was inversely associated with OM (hazard ratio [HR] 0.96, 95% confidence interval [CI], 0.94–0.98; P < 0.01) and CSM (HR 0.96, 95% CI, 0.94–0.99; P = 0.01). Non-linear modelling showed the greatest benefit in OM at between 10 and 20 LNs, but continued survival benefit for OM and CSM beyond 20 LNs. Conclusions: Greater LNC during PC-RPLND appears to be associated with improved CSS and OS in NSGCT. Our data support the role of thorough RPLND for post-chemotherapy metastatic NSGCT.