Impact of Variant Histology on Oncological Outcomes in Upper Tract Urothelial Carcinoma: Results From the ROBUUST Collaborative Group

Introduction: Oncologic implications of variant histology (VH) have been extensively studied in bladder cancer; however, further investigation is needed in upper tract urothelial carcinoma (UTUC). Our study aims to evaluate the impact of VH on oncological outcomes in UTUC patients treated with radical nephroureterectomy (RNU). Methods: A retrospective analysis was performed on patients who underwent a robotic or laparoscopic RNU for UTUC using the ROBUUST database, a multi-institutional collaborative including 17 centers worldwide. Logistic regression was used to assess the effect of VH on urothelial recurrence (bladder, contralateral upper tract), metastasis, and survival following RNU. Results: A total of 687 patients were included in this study. Median (IQR) age was 71 (64-78) years and 470 (68%) had organ confined disease. VH was present in 70 (10.2%) patients. In a median follow-up of 16 months, the incidence of urothelial recurrence, metastasis, and mortality was 26.8%, 15.3%, and 11.8%, respectively. VH was associated with increased risk of metastasis (HR 4.3, P <.0001) and death (HR 2.0, P =.046). In multivariable analysis, VH was noted to be an independent risk factor for metastasis (HR 1.8, P =.03) but not for urothelial recurrence (HR 0.99, P =.97) or death (HR 1.4, P =.2). Conclusion: Variant histology can be found in 10% of patients with UTUC and is an independent risk factor for metastasis following RNU. Overall survival rates and the risk of urothelial recurrence in the bladder or contralateral kidney are not affected by the presence of VH.