Kim H, Son SM, Woo CG, et al. - Primary gastric adenocarcinoma tumors vs corresponding cell blocks prepared from malignant effusions (CB-MEs) were compared regarding human epidermal growth factor receptor 2 (HER2) status. Among the 45 included patients, gastric cancer patients with malignant effusions had very low HER2 positivity rate. Findings suggest discordance in HER2 positivity between the primary gastric adenocarcinoma and corresponding CB-MEs and among serially sampled CB-MEs. Analysis of the primary gastric adenocarcinoma tumor, as well as all the available CB-MEs from each patient, may improve the detection of HER2 positivity.