Objectives: To develop and externally validate a model that quantifies the likelihood that a pathologically node-negative patient with clear cell renal cell carcinoma (cRCC) has, indeed, no lymph node metastasis (LNM). Patients and methods: Data from 1389 patients treated with radical nephrectomy (RN) and lymph node dissection (LND) were analyzed. For external validation, we used data from 2270 patients in the Surveillance, Epidemiology and End Results (SEER) database. We estimated the sensitivity of pathologic nodal staging using a beta-binomial model and developed a pathological nodal staging score (pNSS), which represents the probability that a patient is correctly staged as node negative as a function of the number of examined lymph nodes (LNs). Results: The mean and median number of LNs removed were 7.0 and 5.0 (standard deviation, SD 6.6; interquartile range, IQR 7.0) in the development cohort and 5.6 and 2.0 (SD 8.6, IQR 5.0) in the validation cohort, respectively. The probability of missing a positive LN decreased with increasing number of LNs examined. In both the validation and the development cohort, the number of LNs needed for correctly staging a patient as node negative increased with higher pathological tumor stage and Fuhrman grade. Conclusions: The number of examined LNs needed for adequate nodal staging in cRCC depends on pathological tumor stage and Fuhrman grade. We developed here and then externally validated a pNSS, which could help to refine patient counseling, decision-making regarding risk-stratified surveillance regimens and inclusion criteria for clinical trials of adjuvant therapy.
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