Presentation Authors: Heather Chalfin*, Stephanie Glavaris, Michael Gorin, Max Kates, Megan Hoi Yan Fong, Trinity Bivalacqua, Michael Johnson, Kenneth Pienta, Noah Hahn, David McConkey, Baltimore, MD
Introduction: Despite considerable advances in treatment of urothelial carcinoma (UC), metastatic disease remains life-threatening and the gold standard of cystectomy is a morbid procedure. An acute need exists for platforms that can improve risk-stratification and enhance detection of minimal residual disease as a means to prolong survival and avoid overtreatment. Two such emerging &[Prime]liquid biopsy&[Prime] platforms are circulating tumor cells and DNA (CTCs and ctDNA), yet the application of these tests to UC has not been well-described to date. For ctDNA, it is unclear whether a personalized targeted assay (as has been previously described) is necessary or whether a gene panel may suffice. Here, we compared the performance of these biologically distinct assays in a cohort of metastatic patients.
Methods: CTCs were defined as cytokeratin (CK) or EpCAM positive with the RareCyte selection-free immunofluorescent staining platform. ctDNA was assayed with the PlasmaSelect64 assay, a probe capture NGS panel with 1000x coverage. Matched tissue specimens were sequenced with elio Tissue Complete.
Results: Matched CTC and ctDNA samples were collected for N=16 patients. For 5 patients, 3 replicate time points were collected. Median (range) CTC count was 2.5 (0-170/7.5mL peripheral blood) and number of detected somatic mutations was 2 (0-7). 75% (12/16) patients had detectable CTCs, and 73% (11/15) patients had detectable somatic mutations, similar to the published parameter of 24/37 (67%) ctDNA detection in metastatic UC with a custom designed panel (Wyatt et al Vancouver). Median cell free DNA (cfDNA) yield was 9.03 ng/mL consistent with prior reports of a lower frequency of ctDNA in advanced bladder cancer as opposed to other malignancies. Multiple comparisons of CTC count to ct/cfDNA failed to produce any relationship. We discovered a similar genomic landscape to that which has been published in the past, with frequent mutations in TP53, TERT, and ERBB2.
Conclusions: CTC and ctDNA assays provided distinct and complimentary results. Both liquid biopsies show promise in urothelial cancer and deserve further investigation. A ctDNA assay using a gene panel had similar detection sensitivity in a metastatic UC cohort when compared to a previously described custom patient mutation assay.
Source of Funding: Greenberg Bladder Cancer Institute