Abstract
A case report is presented of a patient diagnosed with esophageal adenocarcinoma with an extremely aggressive clinical course. Discordant expression of HER2 in longitudinally-collected biopsies was noted, with the original biopsy testing negative and a follow up biopsy testing positive. Upon retest of the original biopsy however, heterogeneity of HER2 expression was found among tumor clones across three distinct fields. The patient did not survive long enough to receive chemotherapy with trastuzumab, which has shown efficacy in tumors with HER2 positive expression. Understanding of the biological heterogeneity of HER2 expression in the primary tumor is crucial to detect HER2 positive clones, which may yield improved patient outcomes.