Abstract
Background: Human epidermal growth factor receptor type 2 (HER2) is overexpressed in approximately 20–30% of breast cancer patients who can be treated with anti-HER2 agents, such as trastuzumab, lapatinib, pertuzumab, and trastuzumab emtansine. HER2 overexpression or its absence is thus important in diagnosing and treating breast cancer. HER2 expression is currently evaluated histopathologically; however, the clinical utility of a serum HER2 test remains unclear. We examined the significance of measuring serum HER2 level for indicating the clinical condition of tissue HER2-negative breast cancer patients. Methods: We assessed 210 breast cancer patients whose serum HER2 levels were measured during routine care. The relationships of serum HER2 level with clinical stage and treatment effects were evaluated. The relationships of serum HER2 level with tumor diameter, distant metastasis, and CA15-3 level were evaluated in tissue HER2-negative breast cancer patients. Results: Lower serum HER2 levels were related to greater treatment effects. Correlations were observed between tumor diameter and serum HER2 level (r = 0.485, p < 0.001). The serum HER2 levels in patients with distant metastasis were observed to be significantly higher (p = 0.007). A strong correlation was observed between serum HER2 and CA15-3 levels (r = 0.933, p < 0.001). Conclusions: Serum HER2 is detected in tissue HER2-negative breast cancer patients, and the clinical utility of measuring serum HER2 level as an auxiliary test during routine care is suggested.
