Fig. 1

Representative cases with discordant HER2 status between the primary gastric adenocarcinoma tissue and the CB-ME. The endoscopic biopsy sample of the primary gastric adenocarcinoma from one patient showed HER2 negativity (a; IHC score, 1; original magnification, × 400; scale bar, 50 μm), but the CB-ME showed strong membranous staining (b; IHC score, 3; original magnification, × 400; scale bar, 50 μm), and HER2 gene amplification was detected by SISH (c; original magnification, × 400; scale bar, 50 μm). In another patient, the endoscopic biopsy sample of the primary gastric adenocarcinoma showed strong HER2 expression (d; IHC score, 3; original magnification, × 200; scale bar, 100 μm), but the CB-ME showed no membranous reactivity in any tumor cell (e; IHC score, 0; original magnification, × 400; scale bar, 50 μm). HER2, human epidermal growth factor receptor 2; CB-ME, cell block of malignant effusion; IHC, immunohistochemistry; SISH, silver in situ hybridization