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Status of tissue expression and serum levels of HER2 in gastric cancer patients in Japan.

BACKGROUND
The incidence of HER2 expression in gastric cancer varies among previous studies. Furthermore, serum HER2 levels have not been well studied in patients with gastric cancer.


METHODOLOGY
Cancerous gastric tissue was analyzed by immunohistochemistry (IHC) to give an IHC score (IHC0, 1+, 2+ or 3) for HER2 expression. Fluorescence in situ hybridization (FISH) was performed to examine HER2 gene expression in IHC2+ cases. Levels of HER2 in serum collected before surgery were determined by chemiluminescent enzyme immunoassay.


RESULTS
Subjects were 105 gastric cancer patients who underwent surgical resection. Tissue expression of HER2 was positive (IHC3+, or IHC2+ plus FISH+) in 6.7% of patients (7/105). All HER2-positive tumors were highly differentiated. Mean serum HER2 level was 8.7±2.1 ng/dl in patients with primary gastric cancer. The mean serum HER2 level in the highly differentiated cancer group was 9.2±2.1 ng/dl, which was significantly higher than that (8.1±1.9 ng/dl) in the poorly differentiated group.


CONCLUSION
Tissue expression of HER2 was found in 6.7% of examined Japanese gastric cancer patients, and all HER2-positive tumors were highly differentiated. Serum HER2 levels were significantly higher in patients with highly differentiated cancer, in good agreement with the higher tissue expression of HER2 in highly differentiated cancer.