Comparison of survival outcomes in patients with metastatic papillary vs. clear-cell renal cell carcinoma: a propensity-score analysis

Background: To compare survival outcomes of metastatic patients harbouring either papillary (pRCC) or clear-cell (ccRCC) renal cell carcinoma in overall population and according to treatment modality. Methods: Within the Surveillance, Epidemiology and End Results database (2006–2015), we identified 6800 patients (585 papillary and 6215 clear-cell) with metastatic RCC. Propensity-score (PS) matching, Kaplan–Meier plots and multivariable Cox-regression models (CRMs) were used. Results: Overall, 585 (8.6%) patients harboured pRCC. Rates of nodal metastases were higher in patients with pRCC (49.7 vs. 23.3%; p < 0.001). Median overall survival (OS) was 13 vs. 18 months for pRCC vs. ccRCC patients. After multivariable adjustments, no difference in OS was recorded. Furthermore, after propensity-score matching, virtually the same results were recorded. Median OS of pRCC vs. ccRCC was 8 vs. 4 months for no treatment (NT), 11 vs. 12 months for targeted therapy alone (TT), 17 vs. 35 months for cytoreductive nephrectomy alone (CN) and 18 vs. 25 months for combination of CN with TT. Conclusions: Metastatic pRCC patients exhibit poor survival, regardless of treatment received. Moreover, pRCC patients are more likely to present nodal metastases, compared to ccRCC patients, as demonstrated by twofold higher rates of lymph node invasion at diagnosis. These observations indicate that papillary variant represents more prognostically unfavorable tumor histology, in the context of metastatic RCC.