The lymphatic vessels converge into regional sites containing nests of lymph nodes. The lymph nodes, or glands, filter the lymph fluid for infectious agents and mount an immune response against it. They are part of the immune system. Cancer can spread by way of the lymph vessels and clog up the lymph nodes and start to grow. Often the success or failure of being able to cure a cancer depends on whether the lymph nodes have cancer in them.
Cancer is thought to arise in a single cell.
The location of that cell is the site of the primary cancer. Cancers are named for the primary site of origin, i.e., skin, colon, breast, brain, etc. If a cancer is found in the liver that originated in the colon it is called metastatic colon cancer to the liver not a liver cancer. Liver cancers are those that originated there. If a liver cancer spreads to the lung it is still liver cancer, not lung cancer.