Circulating tumor DNA profiling of advanced biliary tract cancers
Blood tests for tumour DNA found a mutation in three quarters of 124 patients with advanced bile duct or gallbladder cancer and a drug-relevant change in about half, showing the approach is feasible when tissue is hard to get.
Overview
From January 2015 to February 2018, 124 patients with locally advanced or metastatic biliary tract cancer at the Mayo Clinic underwent circulating tumour DNA testing with a clinically available assay, most (n = 122) on a 73-gene panel; about 70% had intrahepatic disease. 138 samples were included.
Excluding variants of unknown significance, 105 samples (76%) had one or more alterations, with an average of three alterations per sample and a median allelic fraction of 0.52%. Therapeutically relevant alterations were observed in 76 patients (55%), including BRAF mutations, ERBB2 amplifications, FGFR2 fusions, FGFR2 mutations and IDH1 mutations seen in 21% of patients. A different spectrum was observed in patients under 50.
- 76% of 138 plasma samples carried at least one alteration; median allelic fraction 0.52%.
- Therapeutically relevant alterations in 55% of patients, including ERBB2 amplification, BRAF, FGFR2 and IDH1.
- Different alteration spectrum in patients under 50.
Biliary tumours are often diagnosed on tiny biopsies or brushings, so a blood-based panel that detects HER2 amplification and other targets in half of patients is a practical route to testing, with tissue confirmation where the blood is uninformative.
- Single centre, predominantly intrahepatic; gallbladder cancers were a minority.
- Plasma panel (Guardant360) of 73 genes; low allelic fractions mean negatives do not exclude a tissue alteration.
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