Impact of variant histology in the prognosis of non‑muscle invasive bladder cancer with low‑tumor burden: A propensity score‑matched analysis with conventional urothelial carcinoma

Bladder cancer (BCa) with variant histology (VH) is associated with an increased risk of recurrence and progression, as well as worse survival. However, the available literature does not provide the prognostic value of VH based on its tumor burden in non-muscle invasive BCa (NMIBC). The purpose of the present study was to investigate the prognosis of VH in NMIBC with low-tumor volume compared with conventional urothelial carcinoma (UC) with a similar tumor burden. The present single-center study analyzed patients diagnosed with NMIBC and retrospectively characterized them based on their VH status. Propensity scores for VH status were calculated to match patients with VH with those with conventional UC (1:3). The VH group was further divided into two subgroups based on pathological aggressiveness: Aggressive and highly aggressive variants. Oncological outcomes were compared among the three groups. Among the 494 patients with NMIBC, 60 (12.1%) had VH. Patients with VH had a higher tumor stage and grade and more multiple tumors (all P<0.05). In the matched cohort, >80% had tumors <3 cm, and >65% had solitary tumors. During a median follow-up of 42.5 months (range, 4.0-122.0 months), 35.1% (85/240) experienced recurrence and 5.4% (13/240) progressed to muscle-invasive disease. Prognosis did not differ between patients with aggressive or highly aggressive variants and those with conventional UC, including 5-year recurrence-free and pathologic progression-free survival (log-rank, P=0.510 and 0.257, respectively). Intravesical Bacillus Galmette-Guerin was the only factor associated with reduced recurrence (P<0.001). In conclusion, NMIBC with low-tumor burden and VH have similar oncologic outcomes to conventional UC with a similar tumor burden, indicating that bladder-sparing methods currently used for high-risk conventional NMIBC may be effective for managing low-tumor burden NMIBC with VH.