held in San Diego, CA between October 1st and 4th, 2023 was host to a session on miscellaneous genitourinary topics. Dr. Shang-Bin Qin presented the results of an analysis evaluating stereotactic ablative radiotherapy (SABR) boost to bladder tumor for bladder preservation in patients with muscle invasive bladder cancer (MIBC).
Dr. Qin began by noting that trimodal therapy has become an established therapy for select patients with muscle invasive bladder cancer, with a recent multicenter analysis by Zlotta et al. demonstrating that trimodal therapy was associated with comparable 5-year metastasis-free survival rates compared to radical cystectomy (~75%) in patients meeting the following eligibility criteria:1
- Solitary tumors <7 cm
- No or unilateral hydronephrosis
- No extensive or multifocal carcinoma in situ
However, despite encouraging long-term outcomes, the 5-year local recurrence rate in the bladder is close to 40% after trimodal therapy. It has been hypothesized that one possible reason for this may be an insufficient radiotherapy dose to the bladder tumor. Stereotactic body radiotherapy (SABR) at ≥6 Gy/fraction has been found to be a safe and effective treatment approach that provides satisfactory local control. As such, the investigators hypothesized that an SABR boost in this setting may improve local control rates. The objective of this study was to report the efficacy and safety outcomes of SABR boost in trimodal therapy for bladder preservation at a single institution.
This was a prospective study that included patients with cT2-4aN0M0 urothelial carcinoma of the bladder. Prior to CT simulation, the tumor site was marked by circumferential lipiodol injections
Saline was subsequently instilled into the bladder via a urethral catheter to achieve adequate bladder filling. SABR was administered to the tumor or tumor bed in the filling bladder, followed by conformal radiotherapy to the pelvic lymph nodes and the empty bladder.
The general treatment schema for trimodal therapy in this study is summarized in the schematic below. Briefly, patients underwent a maximal TURBT, followed by SABR (18 Gy in 3 fractions) delivered to the tumor or tumor bed in the filling bladder. Patients subsequently underwent conformal radiotherapy to the pelvic lymph nodes and empty bladder at a dose of 45 Gy in 25 fractions, with concurrent weekly gemcitabine. Patients without evidence of a complete response or an invasive recurrence underwent a salvage radical cystectomy.
This study included a total of 60 patients, with a median age at diagnosis of 76 years. Almost 50% had cT3-T4 disease, highlighting the high-risk nature of this cohort. Hydronephrosis was present in 15%. Only 42% had a visibly complete TURBT. 56% received pelvic radiotherapy and concurrent chemotherapy was given to 63%.
At a median follow-up of 28 months, the 3-year local control rate was 92%, which is significantly improved compared to historic series. Notably, of patients alive at time of analysis, 97% were disease free and had an intact bladder (2 patients received salvage cystectomy). The 3-year cancer-specific survival rate was 80% and 24% had distant metastases by 3 years.
The 3-year overall survival was 74% among patients who received concurrent chemoradiotherapy (62% in the overall cohort):
With regards to toxicity, acute grade 3 GI and GU toxicities occurred in 1.6% of patients, respectively. There were no grade 3 events. 5% of patients had late grade 3 genitourinary toxicities.
Dr. Qin concluded her presentation with the following take home messages:
- SABR boost followed by chemoradiation to the pelvis achieved an adequate local control rate at 3 years (92%) and was well-tolerated
- Overall survival in a subgroup of patients receiving concurrent chemoradiotherapy was comparable to those of previous bladder preservation studies.
- Given that distant metastasis was a ‘critical mode of failure’, this suggests that patients receiving trimodal therapy may benefit from adjuvant systemic therapy, such as immunotherapy.
Presented by: Dr. Shang-Bin Qin, MD, Department of Radiation Oncology, Peking University First Hospital, Beijing, People’s Republic of China
Written By: Rashid K. Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2023 American Society for Therapeutic Radiation Oncology (ASTRO) 65th Annual Meeting held in San Diego, CA between October 1st and 4th, 2023
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