In medicine, if a cancer originates in a tissue or organ, we usually name it after that tissue or organ. When a cancer originates in the thyroid gland, we name it thyroid cancer. Most of the so-called carcinomas are caused by the metamorphosis or rebellion of individual cells or cell groups in our body, where the growth and development of the metamorphic cells are suddenly out of control and begin to multiply irregularly. As the number of cancer cells multiplying increases, they gather together and increase in size, thus forming cancerous nodules in the body. Some cancerous cells with particularly strong ability to survive and reproduce in the wild can also leave their homeland and travel far away from home. They can first withstand the blows of normal police cells, also known as immune cells, or escape from multiple immune barriers in the body and successfully reach other parts of the body through the normal transportation system of lymphatic vessels or blood, and seed in many tissues and organs, which is what we often call cancer metastasis in medicine or cancer spread. Whenever the cancer cells originating from thyroid cancer spread, we call it thyroid cancer metastasis.