Metastatic cancer refers to the process of tumor cells invading lymphatic vessels, blood vessels or other pathways from the primary site and continuing to grow in other sites to form the same type of tumor as the primary site, the process is called metastasis, and the formed tumor is called metastatic tumor or metastatic cancer. Metastasis is an important feature of malignant tumors. Common metastatic pathways include lymphatic tract metastasis, bloodstream metastasis, implantation metastasis, etc. Once cancer cells invade lymphatic vessels, they can be shed to form emboli or proliferate within the vessels to form continuous masses. Most of the cancer cells will enter regional lymph nodes and form intra-lymph node metastasis.