TACSTD2 and breast carcinoma: As one of the tumor markers that has attracted tremendous focus for ADC drug development, Trop-2, also known as tumor-associated calcium signal transducer 2 (TACSTD2), is a cell surface glycoprotein that is highly expressed in malignant tumors such as breast cancer, colon cancer, pancreatic cancer, and gastric cancer with a regulatory role in tumor cell self-renewal, proliferation, and transformation [3,4].