Figure 1.

Examples of discrepancies of HER2 FISH status between primary breast cancers and matched distant metastases. HER2 (gene encoding human EGF-like receptor 2) fluorescence in situ hybridisation (FISH) status on histological specimens (a, c, e) and matched cytologies of distant metastases (b, d, f). (a, b) Discrepancy due to interpretational difficulty. High-level amplification in primary tumour (a), and rare amplified metastatic cells in pleura effusion that had been overlooked (b). (c, d) Discrepancy due to heterogeneity. Rare tumour cells (arrow) with amplification in the primary breast cancer (c), and metastatic cells in pleural effusion with amplification (d). (e, f) True discrepancy. HER2-negative primary breast cancer (e), and amplification in metastatic cells (f). Original magnifications ×630 to 1,000.