Performance characteristics of a tumor-informed circulating tumor DNA (ctDNA) minimal residual disease (MRD) assay in invasive bladder cancer in clinical practice.

Abstract

542 Background: Detection of minimal residual disease (MRD) is emerging as a potential risk stratification and surveillance tool in patients with resected bladder cancer to potentially direct adjuvant therapy and early intervention. Recently, the sensitivity of MRD testing for early detection of recurrence has been questioned. We sought to evaluate the real world diagnostic performance characteristics of the Signatera ctDNA assay in patients with stage 1-4 bladder cancer who either had transurethral resection of bladder tumor (TURBT) in addition to either chemoradiation or radical cystectomy. Methods: Patients with bladder cancer who underwent ctDNA MRD testing after resection for stage 1-4 disease from 03/2021 to 09/2022 were evaluated retrospectively. Both patients with single and serial ctDNA assays were included. Individual chart review was performed to collect demographic and clinical variables such as diagnosis, stage, pathology, imaging results, and treatment course. Results: MRD results from 19 patients were available, 9 of which had serial assays. 13/19 patients were found to have ctDNA positive results at any time point. The positivity rate at initial testing was associated with stage: Stage 1: 3/5 patients, of which 2 had TURBT and 1 Radical cystectomy, stage 2: 2/5, stage 3: 6/8, and stage 4: 0/1. Notably, of the 9 patients with serial assays, one patient’s result converted from negative to highly positive during surveillance, with subsequent decrease to low positive after adjuvant therapy. One patient had a result of 2 consecutive low positives initially, which was converted to negative after systemic therapy and radiation. 7/19 patients completed testing 3 or more times over a span of approximately 4-13 months, 2 of whom had negative results throughout. Most patients who were found to have positive ctDNA did demonstrate radiographic recurrence within 2-3 months of ctDNA detection. Conclusions: Positive ctDNA MRD after resection is common in bladder cancer. Tumor-informed ctDNA MRD testing has very high sensitivity, but a one-time negative test result does not exclude the presence of metastatic disease. The above data shows an association between cancer stage and positivity results, particularly for advanced stages. Stage I cases with positive results can likely be explained by inadequate resection. Increases in ctDNA may represent early recurrence and can potentially be salvaged with early systemic therapy reverting to negative ctDNA. Prospective randomized and non-randomized studies are evaluating the clinical utility of ctDNA MRD testing in bladder cancer, and analysis of Signatera ctDNA assays will largely contribute to these efforts.