Heterogeneity Influences Cancer Immunohistochemistry Results

Many gastric cancer (GC) patients are with inoperable lesions and endoscopic biopsy becomes the only available approach to obtain tumor tissues for human epidermal growth factor receptor 2 (HER2) assessment. Unlike resected specimens, biopsy specimens are influenced by many factors and in turn more difficult to manipulate.

Several approaches are available for HER2 status assessment, including immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and silver in situ hybridization (SISH). Among them, IHC represents an effective and robust test that can be used for most specimens. HER2 assessment in biopsy specimens of gastric cancer (GC) is challenging because of the intratumoral heterogeneity. False negative results may occur because of limited biopsy material.

Pathologists at Fudan University (Shanghai, China) collected 890 biopsy specimens and 459 paired resected specimens from patients who were diagnosed gastric adenocarcinoma by endoscopic biopsy specimens during March 2013 to January 2014. IHC staining of HER2 was performed. HER2 IHC positive (scored 3+) rate was compared based on tumor-containing fragment number, biopsy specimen number, average size and tumor tissue proportion of tumor-containing fragments. The positive predictability of biopsy specimens to resected specimens was analyzed based on tumor fragment number.

The scientists used a HER-2/neu rabbit monoclonal antibody, and the IHC staining was performed in all the cases with Ventana’s iView DAB Detection Kit on their BenchMark XT automated stainer. For each test, small pieces of GC tissue in which HER2 was scored as 3+ and 0 were used in the same slide as positive and negative controls, respectively. Hematoxylin and eosin (HE) sections of all the cases were reviewed by two experienced gastrointestinal pathologists to confirm the diagnosis.

The team found classified 100 patients (11.2%) as HER2 IHC positive (scored 3+), 261 patients (29.3%) were HER2 equivocal (scored 2+). The rest 529 cases were classified as HER2 IHC negative (59.5%), including 289 cases scored 1+ (32.5%) and 240 cases scored 0 (27.0%). In the HER2 IHC positive (scored 3+) patients, 74 cases were intestinal type GCs (74.0%), 10 were diffuse type GCs (10.0%), and the rest 16 belonged to mixed type (16.0%). HER2 IHC positive rates were 2.0%, 3.5%, 7.0%, 13.2%, 17.1%, and 15.9% when tumor fragment numbers were 1, 2, 3, 4, 5 and 6 respectively. HER2 IHC positive rate was not associated with biopsy number, average size of tumor fragments, and tumor tissue proportion of tumor fragments) directly.

The authors concluded that tumor-containing fragment number affects HER2 IHC positive (scored 3+) rate in endoscopic biopsy specimens. Greater than or equal to four tumor fragments give better HER2 IHC positivity and better performance in predicting HER2 status of resected specimens. The study was published on May 26, 2017, in the journal Diagnostic Pathology.

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