A negative fish test indicates that HER-2 gene expression in breast cancer patients is in a low expression state and there is little benefit from the use of anti-HER-2 targeted drugs. The HER-2 gene is a common oncogene in the survival and development of breast cancer cells, and has the characteristic of promoting the growth of cancer cells. Currently, routine immunohistochemistry is performed on the tissues of breast cancer patients, and when a patient’s HER-2 result is (++), it indicates that the patient is suspiciously positive for HER-2 and requires further examination. fish, also known as fluorescence in situ hybridization, can accurately detect the patient’s HER-2 gene expression. fish negative indicates that the patient does not express or has low expression of HER-2, and may be insensitive to anti-HER-2 therapy with little benefit. FISH positive patients are recommended to undergo anti-HER-2 therapy, such as trastuzumab, patuximab and neratinib. Specific medications and treatments should be prescribed by a physician.