Background: Fluorescence in situ hybridization (FISH) is the gold standard for assessing HER-2 status for breast cancers, and paraffin-embedded tissue sections are used routinely for HER-2 FISH. Cytologic samples also are used, but to the authors' knowledge, little is known regarding the reliability of these samples. The objective of this study was to elucidate the usefulness of cytologic specimens for HER-2 FISH testing.
Methods: Histologic and cytologic specimens from 32 patients with invasive ductal carcinoma of the breast were subjected to comparative analysis of HER-2 status by FISH. FISH was performed by using a PathVysion HER-2 DNA Probe Kit according the manufacturer's instructions. The signal ratios of chromosome enumeration probe 17 (CEP17) and HER-2 were estimated and compared. In 15 cytologic specimens, the distance between signals (HER-2 and CEP17) and the nearest nuclear membrane were measured by using 3-dimensional image analysis and confocal microscopy.
Results: Cytologic and histologic FISH results were compared. Signal ratios of HER-2/CEP17 were lower in cytologic specimens from 26 of 32 patients compared with the histologic material. Three-dimensional image analysis demonstrated that the distance between the CEP17 signal and the nuclear membrane was shorter than the distance between the HER-2 gene and the nuclear membrane.
Conclusions: The current results demonstrated that CEP17 could be lost more easily through histologic sectioning compared with the cytology results, because CEP17 is closer to the nuclear membrane. FISH analysis in cytologic specimens produced more accurate HER-2/CEP17 ratios, because the whole nucleus was subjected to FISH testing, compared with matched histologic specimens.
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