Concordance of Circulating Tumor DNA, Primary and Metastatic Tissue DNA, and Immunohistochemistry in Gastroesophageal Carcinoma.

Among 345 patients with ctDNA testing, 186 had tDNA testing, and 310 underwent immunohistochemistry. ctDNA testing showed a shorter turnaround time than tDNA (median 6 v 13 days).

The most frequent alteration in ctDNA, primary tDNA, and metastatic tDNA was TP53.

IHC-ctDNA concordance was higher in metastatic tumors, with 91.1% for HER2/ ERBB2 and 97.7% for mismatch repair (mismatch repair)/microsatellite instability (microsatellite instability) compared with 81.1% and 95.8%, respectively, in primary tumors.