Efficacy and tolerance of hyperthermic intravesical chemotherapy (HIVEC) according to the number of instillations administered.

Purpose: To report the oncological outcomes and the tolerance between 6 instillations and more than 6 cycles of hyperthermic intravesical chemotherapy(HIVEC) in patients with non-muscle invasive bladder cancer(NMIBC).

Methods: This is a multicenter retrospective study from a national database including 9 expert centers. All patients treated with HIVEC between 2016 and 2023 for NMIBC were included. Patients were classified into two groups according to the total number of HIVEC instillations, including induction plus maintenance. Kaplan-Meier curves were computed to present survival outcomes.

Results: 261 patients with a median follow-up of 25.5 months were included. 199(76.2%) and 62(23.8%) were treated by 6 and more than 6 cycles of HIVEC, respectively. The 2-years RFS(40.2% vs. 34.4%,p = 0.3) and the 2-years PFS(86% vs. 87%,p = 0.85) were similar between group treated with 6 and more than 6 instillations. 2-years CSS and OS were also similar between both groups. Univariate Cox regression showed no association between the number of bladder instillation and RFS (HR = 1.2 95%CI[0.8-1.84], p = 0.3) or PFS (HR = 0.8 95%CI[0.29-2.02], p = 0.2). In the group treated with more than 6 cycles, 2-years RFS and 2-years PFS were similar between patients who received induction plus maintenance compared to those treated with induction only. Finally, hematuria and urinary burning were significantly higher in the group treated by more than 6 cycles (21% vs. 8.5%(p < 0.01),and 29% vs. 17% (p = 0.03), respectively). Serious side effects(grade ≥ 3) are rare(3.1%) and similar in both groups.

Conclusions: Results show no significant difference in two years RFS, PFS, CSS and OS according to number of instillations received, while toxicity profile seems better in the group receiving six instillations only.