Detection of an Fusion in Colorectal Carcinoma by Hybrid Capture-Based Assay of Circulating Tumor DNA.

UNLABELLED

rearrangements have been observed in 0.05%-2.5% of patients with colorectal cancers (CRCs) and are predicted to be oncogenic drivers largely mutually exclusive of or alterations. Here we present the case of a patient with metastatic CRC who was treatment naïve at the time of molecular testing. Initial ALK immunohistochemistry (IHC) staining was negative, but parallel genomic profiling of both circulating tumor DNA (ctDNA) and tissue using similar hybrid capture-based assays each identified an identical fusion. Subsequent ALK IHC staining of the same specimens was positive, suggesting that the initial result was a false negative. This report is the first instance of an fusion in CRC detected using a ctDNA assay.

KEY POINTS

Current guidelines for colorectal cancer (CRC) only recommend genomic assessment of and microsatellite instability (MSI) status. rearrangements are rare in CRC, but patients with activating fusions have responded to targeted therapies rearrangements can be detected by genomic profiling of ctDNA from blood or tissue, and this methodology may be informative in cases where immunohistochemistry (IHC) or other standard testing is negative.