How Many Lymph Nodes are Enough in Paratesticular Rhabdomyosarcoma?

Background: Treatment strategies for paratesticular rhabdomyosarcoma (PT RMS) are based on stage, which requires accurate lymph node (LN) evaluation. Previous methodology for determining quantity of LN for negative nodal status is based on LN positivity rates, without accounting for the relationship between LNs or amongst patients. This study aims to quantify the chance of missing involved LNs based on LN yield (LNY) using a previously established methodology in comparison to current recommendations. Methods: Using the National Cancer Database, patients with a diagnosis of PT RMS were queried from 2004 to 2018. Patients >10 years and those ≤10 years with cN1 disease were included, based on COG guidelines for who should undergo retroperitoneal LN sampling (RPLNS). The beta-binomial model was used to calculate the rate of false negative RPLNS and identified the LNY threshold to reduce the risk of a missing an involved LN node to <10 %. Results: Sixty-two patients were included for analysis over the study period. Median LNY was 17 (IQR 9–28.75), and the median number of involved LNs was 2.5 (IQR 2–5). The median LN density was 0.27 (IQR 0.10–0.34). Application of the beta-binomial model identified that a LNY of 26 LNs corresponds to a <10 % chance of missing occult disease (Fig. 3). Conclusion: Previous models estimate that sampling of 7–12 LN is adequate for accurate staging. However, the beta binomial model quantifies sampling at least 26 LNs to reduce the chance of missing occult metastatic disease to <10 % in the majority of patients. Surgeons should consider this false negative rate during RPLNS for patients with PT RMS. Level of Evidence: III.