Human trophoblast cell-surface glycoprotein antigen 2 (Trop2) is a membrane surface receptor that plays an important role in the occurrence and development of tumors. Studies have shown that Trop2 is highly expressed in a variety of cancers (such as breast cancer, lung cancer, gastric cancer, colorectal cancer, pancreatic cancer, prostate cancer, cervical cancer, head and neck cancer, and ovarian cancer, etc.) and is related to the proliferation, invasion, and metastasis of tumor cells. and other processes related. According to statistics, more than 80% of breast cancer patients highly express Trop2, and high expression of Trop2 is positively correlated with shortened survival and poor prognosis of cancer patients. In this study, a single-domain antibody targeting Trop2 was selected to prepare a new nuclear medicine molecular probe 99mTc-MY6349, so as to monitor the expression level of Trop2 in patients' systemic tumors through SPECT/CT imaging. Breast cancer patients who intend to use gosatuzumab for subsequent treatment can first undergo 99mTc-MY6349 SPECT/CT imaging to detect Trop2 expression levels in systemic tumors. Subsequently, 18F-FDG PET/CT imaging was performed to compare and detect the distribution of primary tumors and systemic metastases in patients with breast cancer. This study analyzes the heterogeneity of Trop2 expression levels within the primary tumor and the heterogeneity of expression levels in systemic metastases, thereby providing a basis for testing whether the patient is suitable for subsequent treatment and conducive to the formulation of subsequent treatment plans.