Clinical outcomes and mutation analysis of carbon ion radiotherapy for bladder urothelial carcinoma

Carbon–ion radiotherapy (CIRT) improves the survival outcomes in patients with tumor recurrence or metastasis. However, there is little data to support the clinical efficacy of CIRT for bladder cancer. Ten patients underwent CIRT between November 2020 and July 2023 (ChiCTR2100043607). A comprehensive evaluation of the tumor control and toxicity of CIRT was performed, and the clinical characteristics associated with CIRT resistance were analyzed. The median age of the patients was 69 years (range, 32–81) at the start of CIRT, and 90% were male. With a median follow-up of 28 months (range, 18.3–35.6), and 2 patients (20%) developed local recurrence and/or distant metastases. Complete clinical response was achieved in 4 patients (40%), whereas partial response was documented in 4 patients (40%). The 1-year overall survival, progression-free survival, and local progression-free survival rates were 100.0%, 80.0%, 90.0%, respectively. The median prescription dose of CIRT was 70 Gy [relative biological effectiveness (RBE)], ranging from 64Gy (RBE) to 74Gy (RBE). One of the cases harbored mutations associated with CIRT resistance, including ARID1A V1982I, CCND1 S43F, and FANCA C1159S mutations. Moreover, individuals carrying FGFR3 R34Q and PIK3CA E545K mutations showed significant improvement. The acute and late toxicities were grade 2 or lower. No grade III or higher toxicity was observed. CIRT provides favourable tumor control and acceptable toxicity in bladder cancer. Further prospective clinical studies are necessary to use predictive and prognostic biomarkers to evaluate the therapeutic efficacy and adverse events of CIRT in patients with bladder urothelial carcinoma.