External validation of nomogram to predict inguinal lymph node metastasis in patients with penile cancer and clinically negative lymph nodes

INTRODUCTION: Penile cancer (PC) occurs less frequently in Europe and in the United States than in South America and parts of Africa. Lymph node (LN) involvement is the most important prognostic factor, and inguinal LN (ILN) dissection can be curative; however, ILN dissection has high morbidity. A nomogram was previously developed based on clinicopathological features of PC to predict ILN metastases. Our objective was to conduct an external validation of the previously developed nomogram based on our population. MATERIALS AND METHODS: We included men with cN0 ILNs who underwent ILN dissection for penile carcinoma between 2000 and 2014. We performed external validation of the nomogram considering three different external validation methods: k-fold, leave-one-out, and bootstrap. We also analyzed prognostic variables. Performance was quantified in terms of calibration and discrimination (receiver operator characteristic curve). A logistic regression model for positive ILNs was developed based on clinicopathological features of PC. RESULTS: We analyzed 65 men who underwent ILN dissection (cN0). The mean age was 56.8 years. Of 65 men, 24 (36.9%) presented with positive LNs. A median 21 ILNs were removed. Considering the three different methods used, we concluded that the previously developed nomogram was not suitable for our sample. CONCLUSIONS: In our study, the previously developed nomogram that was applied to our population had low accuracy and low precision for correctly identifying patients with PC who have positive ILNs.