What would indicate that a breast cancer is HER2-positive?

The indication that a breast cancer is HER2-positive is associated with elevated levels of the HER2 protein. HER2, which stands for human epidermal growth factor receptor 2, is a protein that can promote the growth of cancer cells. In a small percentage of breast cancers, the cancer cells overly express HER2 or have an amplification of the HER2 gene, leading to aggressive tumor growth. Testing for HER2 positivity is usually done through immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH), which can directly measure the presence and levels of the HER2 protein or gene.

The other options do not logically signify HER2 positivity. Tumor shrinkage with surgery could occur in various types of cancers or even benign conditions and doesn't specifically relate to HER2 status. A patient showing no symptoms makes it impossible to determine HER2 status because it is a cellular characteristic, not a symptomatic one. Lastly, stating that a tumor is always benign does not apply, as HER2-positive tumors are typically aggressive and are often associated with invasive breast cancer.