The main metastatic pathways of osteosarcoma are generally divided into three types. The first is hematogenous spread, which refers to the dispersal of tumor cells throughout the body via the bloodstream, typically settling in areas with slower blood flow which facilitates the deposition of these cells leading to local changes. The second is direct implantation, which involves tumor cells directly establishing themselves in the vicinity of the tumor's common sites, eventually leading to local metastasis. The third type is lymphatic spread, where tumor cells migrate through the lymphatic system, spreading along lymphatic vessels or pathways. Therefore, the main metastatic pathways of osteosarcoma are these three types. The primary sites of metastasis for osteosarcoma are mainly the lungs, but metastases can also occur in the brain or through other mechanisms.