How many lymph nodes are enough for staging in Paratesticular Rhabdo myosarcoma?
Brittany E. Levy, MD1, Will Cranford, MS1, Adam Dugan, PhD1, Christopher McLouth, PhD1, Jonathan Routh, MD2, David Rodeberg, MD1, Amanda F. Saltzman, MD1.
1University of Kentucky, Lexington, KY, USA, 2Duke Univeristy, Durham, NC, USA.
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. This study aims to quantify the false negative rates of LN sampling based on LN yield 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 2004-2018. Patients >10y and those < 10y with clinical N1 disease were included, based on COG guidelines. LN density was calculated using LN yield and the number of involved LNs. Based on established methodology, the beta-binomial model was used to calculate the rate of false neg LN sampling and identified the LN yield threshold to reduce the risk of a missing an involved LN node to < 10%.
Results: 67 patients were included for analysis over the study period. The median number of LNs sampled was 16 (IQR 8-25), and the median number of involved LN was 2 (IQR 1-4). The median lymph node density was 0.3 (IQR 0.1-0.3). For patients in the 1st-3rd quartiles of lymph node yield, < 30 LN are sampled. Application of the beta-binomial model for those with < 30 LN sampled, 13 LNs are needed to reduce the chance of missing an occult involved LN to < 10%. (Figure)
Conclusions: Previous statistical models estimate sampling of 7-12 LN is adequate for accurate staging. However, to account the negative correlation of LN sampled to proportion of involved LN, an alternative statistical analysis is beneficial. As such, the beta binomial model supports sampling at least 13 LNs to reduce the chance of missing occult metastatic disease to < 10% in the majority of patients.
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