Lymph node density as a prognostic marker of relapse in patients who underwent primary retroperitoneal lymph node dissection.

Introduction: Primary retroperitoneal lymph node dissection (pRPLND) is a treatment option for clinical stage (CS) II testicular germ cell tumors (TGCTs) and CS I with retroperitoneal relapse. Increasing raw lymph node yield during pRPLND has been associated a decreased relapse risk. However, this metric has limitations due to variations in surgical templates and specimen processing methods. We aimed to evaluate the lymph node density (LND), which is the ratio of positive lymph nodes to the total number of nodes removed, as a prognostic marker for relapse after pRPLND.

Methods: We reviewed all patients who underwent pRPLND at the Princess Margaret Cancer Centre between 1990 and 2022. The primary endpoint was relapse-free survival (RFS). RFS was calculated using the Kaplan-Meier product-limit method. The log-rank test was used to assess the impact of LND, and recursive binary partitioning was used to determine the threshold LND that provides optimum separation in RFS.

Results: In this study, 178 patients were treated with pRPLND. A total of 137 (77%) patients had pathological evidence of nodal metastasis, 96 were treated with open RPLND, and 41 with robotic RPLND. The median number of lymph nodes harvested was 32 (IQR 23-43) and median total positive nodes was 2 (IQR 1-36). This translated into a median LND of 3.1% (IQR 1.7-57.1). There was no significant difference in the LND between robotic and open approaches (P = 0.6664). After a median follow-up of 38.6 months, 11 patients (8.02%) had relapsed. LND was not significantly associated with relapse (HR 1.018, 95% CI, 0.977-1.061). The optimal threshold to dichotomize LND that provides optimum separation in RFS was ≥ 26.75%, however, it did not reach statistical significance (P = 0.0651).

Conclusion: In conclusion, the LND was not associated with RFS after pRPLND in patients with TGCTs. The unique characteristics of TGCTs and the presence of other established risk factors limit the utility of the LND alone in predicting relapse.