Role of ctDNA to predict risk of recurrence following potentially curative resection of biliary tract and pancreatic malignancies.

Background:
The potential role of ctDNA to identify residual disease after potentially curative resection has been suggested in some malignancies; its role in resected pancreatico(P)-biliary(B) malignancies is unknown.
Methods:
Patients diagnosed with PB malignancies underwent molecular profiling (ctDNA) using FoundationMedicine Liquid (72 cancer-related genes) following potentially curative resection. Baseline patient characteristics and molecular profiling outcomes, including mutant allele frequency (MAF) for pathological alterations were extracted. Primary objective: prevalence of ctDNA identification and its correlation with recurrence (relapse-free survival (RFS) and relapse rate).
Results:
Total of 11 individuals had ctDNA analysed following potentially curative resection for PB malignancies: 8 B (4 extra-hepatic cholangiocarcinoma (eCCA), 2 ampulla, 1 intrahepatic cholangiocarcinoma (iCCA), 1 gallbladder cancer (GBC)) and 3 P. Baseline characteristics: 6 female (54.55%), median age 71.59 years (range 39.98-81.19). Most were pT2 (45.45%), pN0 (54.55%) and R0 (63.64%). Following surgery, 6 patients were started on adjuvant chemotherapy; at the end of follow-up (data cut-off 25/6/2020; median follow-up 11.15 months (range 5.45-13.52); 5 relapsed (45.45%) and 2 died (18.18%). Estimated median RFS was 11.43 months (95% CI 2.28-not reached); median overall survival was not reached. No sample failed ctDNA analysis; presence of ctDNA was identified in 3/11 (27.27%) of the samples; 2 and 1 samples had 2 and 1 pathological alterations identified, respectively: ALK fusion (1 sample; GBC), TP53 mutation (2 samples; eCCA and GBC), CHEK2 mutation (1 sample; pancreas), IDH2 mutation (1 sample; eCCA). Mean maximum MAF was 1.47 (2 in biliary; 0.43 in pancreas). Variants of unknown significance were identified in 72.73% of the samples (87.5% in B; 33.33% in P; p-value 0.152). None of the baseline characteristics explored correlated with presence of ctDNA. There was a trend towards increased relapse risk in the patients with ctDNA present following potentially curative surgery; Cox regression for RFS [HR 2.64 (95% CI 0.36-19.31); median RFS 11.44 months (95% CI 2.28-not reached) vs 10.87 (95% CI 2.21-not reached)]; relapse rate 37.5% (ctDNA absent) vs 66.67% (ctDNA present); statistical significance was not reached (p-value 0.340 and p-value 0.545, respectively).
Conclusions:
This pilot study demonstrates the feasibility of testing for ctDNA following potentially curative resection in PB malignancies. Presence of ctDNA may be associated with increased relapse risk; further studies are required to increase sample size and assess clinical implications.