[370] Comparison of HER2 Gene Status Determination by HER2 Dual ISH DNA Probe Cocktail Assay Performed on Cell Block Material to Immunohistochemistry (IHC) and Fluorescence In Situ Hybridization (FISH) Performed on the Corresponding Histologic Specimen

Adria Hartman, Blythe Gorman, Dina Mody. The Methodist Hospital, Houston, TX

Background: The human epidermal growth factor receptor 2 (HER2) gene is amplified in 18% to 20% of breast cancers. HER2 gene amplification status is important for therapeutic decision making, and The American Society of Clinical Oncology (ASCO) Tumor Marker Guidelines Panel has recommended routine testing of HER2 on newly diagnosed and metastatic breast cancers. Cell block preparations of cytologic material are a valuable tool for determining HER2 gene amplification status on metastatic lesions, which are often sampled by fine needle aspiration (FNA) alone. The INFORM HER2 Dual ISH DNA Probe Cocktail assay by Ventana Medical Systems, Inc., uses two color chromogenic in situ hybridization (CISH) to determine HER2 gene status with light microscopy. This allows for the identification of patients who would benefit from Herceptin (trastuzumab) therapy.
Design: Cytologic samples obtained from fresh resection specimens with biopsy proven invasive mammary carcinoma were processed into three types of cell blocks (Cellient, thrombin, and formalin). The INFORM HER2 Dual ISH DNA Probe Cocktail assay was performed on the cell blocks. The ratio of HER2 to chromosome 17 signals was calculated to determine the HER2 gene amplification status. The HER2 gene amplification status of each biopsy or resection specimen, as determined by IHC and/or FISH, was compared to the results obtained from the assessment of cell blocks analyzed by the HER2 Dual ISH DNA Probe Cocktail assay.
Results: Comparison of HER2 gene status by Dual ISH DNA Probe Cocktail Assay on cell block material showed 100% correlation with the HER2 gene status determined by either IHC or FISH on histologic specimens. Through ongoing process optimization tailored toward cell block material, enumerable signals and ratios were calculated on eight cell blocks, which included three Cellient cell blocks, two formalin cell blocks, and three thrombin cell blocks. All the cases were HER2 gene amplification negative. No false-positive results occurred.
Conclusions: While further validation and study is underway, preliminary results show that breast carcinoma HER2 gene amplification status can reliably be determined on cell block material using The INFORM HER2 Dual ISH DNA Probe Cocktail assay.
Category: Cytopathology

Wednesday, March 21, 2012 1:00 PM

Poster Session VI # 87, Wednesday Afternoon

 

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