SABR Boost May Help Preserve Bladder in Patients With MIBC

Trimodality therapy (TMT) shows favorable results when used as a selective bladder-sparing approach for muscle-invasive bladder cancer (MIBC), with outcomes similar to radical cystectomy. However, the 5-year local recurrence rate remains higher than 40% in patients after receiving TMT, potentially due to an insufficient radiotherapy dose.

To alleviate this issue, an international team of researchers assessed the safety and efficacy of utilizing a stereotactic ablative radiotherapy (SABR) boost to the bladder tumor or tumor bed in patients with MIBC. They presented their results at the American Society for Radiation Oncology 2023 Annual Meeting.

A cohort of 59 patients with cT2-4 bladder cancer were included in the study, and all patients underwent transurethral resection of bladder tumor (TURBT). TURBT was visibly complete in 25 cases. Patients received treatment with SABR to their tumor or tumor bed in the bladder followed by conventionally fractionated radiotherapy to the pelvis and total bladder, with concomitant weekly radio-sensitizing chemotherapy.

To ensure adequate bladder filling during SABR, researchers utilized intravesical instillation of isovolumetric saline through a urinary catheter. The response rate was assessed through cystoscopy and pelvic magnetic resonance imaging or computed tomography. Toxicities were assessed using the Radiation Therapy Oncology Group Acute and Late Radiation Morbidity Scoring Schema.

The median age of the patient cohort was 76 years (range, 35-90 years). Each patient completed a SABR boost, and 61% of patients received concurrent gemcitabine chemotherapy. After a median follow-up of 28 months, the rate of local control was 90.0%, the overall survival rate was 61.6%, and the cancer-specific survival rate was 77.5%.

Of the surviving patients, 84.4% had disease-free and functioning bladders. Acute grade 3 gastrointestinal (GI) or genitourinary (GU) toxicities occurred in only 1.7% of patients, and late grade 3 GU toxicity occurred in 5.1%. No patients experienced grade 4 GI or GU toxicities.

The use of a SABR boost followed by chemoradiation to the pelvis was found to be well-tolerated and effective in patients with MIBC who are either not eligible for cystectomy or who favor bladder preservation. Further randomized studies are needed to verify this novel trimodality treatment paradigm.