Background: Cell-free ctDNA may be potentially actionable, may have prognostic/predictive role and evolve after therapy. We updated our analysis of our retrospective study to shed light on UC/BC biology. Methods: Patients (pts) with UC/BC with ctDNA analysis for potentially actionable alterations using Guardant360 were identified. A 70-gene ctDNA next generation sequencing panel from a CLIA-licensed, CAP-accredited laboratory (Guardant Health, Inc.) offers complete exon sequencing for 29 cancer genes, critical exons in 39 genes and amplifications (16 genes), fusions (6 genes) and indels (3 genes) harvested from 10 mL of peripheral blood. Descriptive statistics were used. Results: There were 246 pts with 276 samples. At least 1 alteration was detected in 249 (90%) samples. Median age at time of ctDNA collection was 67 years (39-85), 78% men, median number of alterations per sample was 3.5 (1-35) most pts had MIBC. In MIBC pts, the most common alterations at the 1st ctDNA sample were in TP53 (52%), PI3KCA (18%) ARID1A (17%), FGFR2 (15%), MET & NF1 (14%), EGFR (13%), BRAF (12%), FGFR3 (11%), RAF1 (10%), BRCA1 & CCNE1 (9%). In MIBC pts, the most common genes with increased copy number were RAF1 & CCNE1 (8%), ERBB2 & PI3KCA (7%), EGFR, BRAF, FGFR1, MYC (each 5%), MET (4%), KRAS (3%). Most common altered pathways included TP53 signaling (56%), RAS/RAF/MEK/ERK (51%), RTK (48%), cell cycle (38%), FGFR family (34%), DNA damage response (25%), PI3KCA/AKT/mTOR (23%) and chromatin remodeling (17%). Interestingly, FGFR3 and RAS alterations were mutually exclusive in most cases, but each may co-occur with TP53alterations. 54 serial ctDNA samples from 24 pts (18 pts with 2 samples; 6 pts with 3 samples) revealed persistent, lost and new gene alterations. Conclusions: ctDNA was detected in 90% of pts and alterations were similar to those previously seen in UC tumor tissue. Tumor heterogeneity, interim therapy, genomic instability and clonal evolution can explain differences in serial samples. Correlation assessment with prior therapies and outcomes is being pursued to inform trial designs. Prospective validation, assessment of ctDNA concordance with tumor tissue DNA, and evaluation of clinical utility is warranted.