External validation of the pathological nodal staging score in upper tract urothelial carcinoma: A population-based...

To externally validate our previously developed pathological nodal staging model (pNSS) that allows quantification of the likelihood that a patient with pathologic node-negative status has, indeed, no lymph node metastasis (LNM).

We analyzed data from 2,768 patients treated with radical nephroureterectomy (RNU) and lymph node dissection (LND) using the Surveillance, Epidemiology, and End Results database from 1988 to 2010. We estimated the sensitivity of pathologic nodal staging using a beta-binomial model and developed a new pNSS. Then, we compared these findings with those of the initial cohort.

The mean and median numbers of lymph node (LN) removed were 5 and 2, respectively (interquartile range = 5) in the validation cohort, though 66.5% of the patients (n = 1814) were pN0. Similar to the development cohort, the probability of missing a LNM decreased as the number of nodes examined increased in the validation cohort. If only a single node was examined, 35% of patients would be misclassified as pN0 while harboring LNM. Even when 5 nodes were examined, 8% would be misclassified. The probability of having a positive node increased with advancing pathological T stage in both the cohorts. Patients with pT0-Ta-Tis-T1 disease in both cohorts would have more than a 95% chance of a correct pathologic nodal staging with 2 examined nodes. However, if a patient has pT3-T4 disease, more than 12 examined LNs are needed to reach 95% accuracy.

We confirmed that the number of examined nodes needed for adequate staging depends on pT category. We externally validated our previous pNSS in a population-based database, which could help in the clinical decision-making regarding adjuvant chemotherapy administration.