The steps of metastasis include a cancer cell breaking off from a primary tumor, moving off to other tissues, entering and making it through blood vessels, making it into lymphatics or peritoneal cavities, and surviving to make a home in a distant organ. It then may form a new lesion.
Cancer cells have four favorite channels by which to travel, including lymphatic channels, blood vessels, body cavities and transplantation of the cancer. Many carcinomas spread through the lymphatic channels, while sarcomas and some carcinomas that start in the kidneys often travel by blood vessels because of a kidney's thinner wall veins. Cancer cells on the lungs, stomach and other abdominal organs, heart and brain like to spread via body cavities. Cancer transplantation can happen when medical tools that have not been sterilized carry parts of tumor cells from one patient to another, or from one part of a patient's body to another part.
Cancer cells encounter a host of dangers while traveling through the body, and many perish during the length of the journey, breaking while traveling through tight spaces, or by being attacked and destroyed by the body's immune system. Cancer cells that make it to their new locations can then start the process again.