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Background: Pathological stage and grade of renal pelvis urothelial carcinoma (RPUC) are difficult to estimate before radical nephroureterectomy (RNU). Objective: To examine tumor size as an independent predictor of muscle-invasive and/or non–organ-confined rates of RPUC at RNU. Design, setting, and participants: Within the Surveillance, Epidemiology and End Results (SEER) database (2004–2016), we identified nonmetastatic RPUC at RNU. Outcome measurements and statistical analysis: First, we examined stage and grade distributions. Second, two separate univariable and subsequent multivariable logistic regression models (LRMs) were fitted to test the association between tumor size and the rate of (1) muscle-invasive or higher (pT2–4N0–2) and (2) non–organ-confined (pT3–4N0–2) RPUC at RNU. Results and limitations: Of 4657 patients, 3052 (65.5%) had pT2–4N0–2 and 2382 (51.2%) pT3–4N0–2 RPUC at RNU. The median tumor size was 3.7 cm (interquartile range 2.5–5.0). The high-grade RPUC rate ranged from 71.1% to 87.2% (p < 0.001) among SEER registries. Conversely, no differences were recorded for stage (p > 0.05) or tumor size (p = 0.1) across all registries. Rates of pT2–4N0–2 and pT3–4N0–2 RPUC increased with tumor size. Specifically, for tumor size intervals from 0.1–1.0 cm to 9.1–10.0 cm, the pT2–4N0–2 rate ranged from 45% to 83% and the pT3–4N0–2 rate ranged from 23% to 75%, respectively (both p < 0.001). In multivariable LRMs, tumor size (in 1-cm units) was an independent predictor of pT2–4N0–2 (odds ratio [OR] 1.25; p < 0.001) and pT3–4N0–2 (OR 1.30; p < 0.001) disease at RNU. Conclusions: Tumor size is a key predictor of muscle-invasive or non–organ-confined RPUC. Greater tumor size directly and virtually linearly predicts a higher rate of invasive or non–organ-confined RPUC at RNU. Patient summary: For patients with cancer in urinary tract cells lining the kidney, larger tumor size predicts worse stage of the disease at surgery.

Background: For patients with nonmetastatic renal cell carcinoma (nmRCC) treated with nephrectomy, prediction of cancer-specific mortality (CSM) by T stage and substage has not been validated for the separate histological subtypes. Objective: To investigate the ability of pathological T stage and substage to predict CSM for patients with clear-cell, papillary, or chromophobe nmRCC treated with nephrectomy. Design, setting, and participants: Using the SEER database for 2004–2016, we identified 87 149 patients with T1–4 N0/X M0 nmRCC treated with nephrectomy for the clear-cell (65 715; 75.4%), papillary (14 587; 16.7%), or chromophobe (6847; 7.9%) histological subtype. Outcome measurements and statistical analysis: Kaplan-Meier plots and Cox regression models were used to estimate CSM. Results and limitations: For all three histological subtypes, patients with T1a–T3a disease exhibited more favorable CSM than patients with T3b–T4 RCC. For clear-cell RCC, there were clinically meaningful and statistically significant differences for virtually all intergroup comparisons among T1a–T3a stages. For papillary T1a–T3a RCC, clinically meaningful differences disappeared, although the statistical significance remained. For chromophobe T1a–T3a RCC, no clinically meaningful or statistically significant differences were observed. For all three histological subtypes, patients with T3b–T4 RCC exhibited virtually uniformly unfavorable CSM, with no clinically meaningful intergroup CSM differences. Conclusion: The use of T stage and substage for stratification of patients with nmRCC treated with nephrectomy revealed differences in CSM among T1a–T3a cases, but not T3b–T4. The magnitude of the CSM difference was greatest for clear-cell, intermediate for papillary, and marginal for chromophobe RCC. Patient summary: For patients with kidney cancer, the stage of their disease assessed after surgery on the affected kidney can predict how likely they are to die from their cancer. This prediction varies for different subtypes of kidney cancer. Stratification of surgically treated patients with nonmetastatic renal cell carcinoma (RCC) by T stage revealed mortality differences among T1a–T3a cases, but not T3b–T4 cases. The magnitude of the differences was greatest for the clear-cell subtype, intermediate for papillary histology, and marginal for chromophobe RCC.