What does tumor spread mean?

Everyone knows that some diseases in the human body will gradually spread to other parts if they are not controlled or treated with drugs, and after spreading to other parts, they will cause more serious consequences. Tumors are a disease that occurs in many people. In fact, if the tumor is not removed or treated, it can easily spread. But what does it mean when a tumor spreads?

The ability to locally invade and metastasize to distant sites is the most important biological characteristic of malignant tumors. Tumors that grow in an invasive manner can not only continue to grow at the primary site and spread directly to the surrounding tissues, but can also spread to other parts of the body (metastasis) through a variety of pathways. This is the main characteristic of malignant tumors.

Tumors that grow in an invasive manner can not only continue to grow at the primary site and spread directly to the surrounding tissues, but can also spread to other parts of the body (metastasis) through a variety of pathways. This is the main characteristic of malignant tumors.

1. Direct spread refers to the growth state in which malignant tumors continuously infiltrate and destroy surrounding tissues and organs. As malignant tumor cells proliferate, they often continuously infiltrate along the tissue spaces, the peripheral spaces of lymphatic vessels and blood vessels, and the neural sheaths, destroying adjacent normal organs and tissues and continuing to grow. For example, pancreatic cancer can spread to the liver and duodenum; advanced breast cancer can spread through the pectoral muscles and chest cavity to the lungs.

2. Metastasis: Malignant tumor cells invade lymphatic vessels, blood vessels or body cavities from the primary site, migrate to other places and continue to grow, forming tumors of the same type as the primary tumor. This process is called metastasis. The tumors formed are called metastatic tumors or secondary tumors.

Transfer pathways

There are the following: (1) Lymphatic metastasis: Malignant tumors originating from epithelial tissues often metastasize through the lymph nodes. After the tumor cells invade the lymphatic vessels, they first reach the local lymph nodes with the lymph flow, gather in the marginal sinus, and continue to proliferate and develop into metastatic tumors in the lymph nodes. For example, breast cancer often metastasizes to the ipsilateral axillary lymph nodes first; lung cancer first metastasizes to the hilar lymph nodes. The metastatic tumor begins to grow from the edge of the lymph node and gradually involves the entire lymph node. The affected lymph nodes gradually become larger and harder, and the cross-section appears grayish white. Sometimes, due to the invasion of tumor tissue beyond the capsule, multiple lymph nodes fuse together to form a mass. After local lymph node metastasis, it can continue to metastasize to other lymph nodes at the next stop, and finally enter the bloodstream through the thoracic duct and continue to metastasize through the blood. Some tumors can undergo retrograde metastasis (troisier sign) or skip metastasis (skip metastasis) across the draining lymph nodes. Clinically, the most common lymph node metastasis is the left supraclavicular lymph node, and its primary site is mostly located in the lungs and gastrointestinal tract.

(2) Hematogeneous metastasis: After malignant tumor cells invade blood vessels, they can flow through the blood to distant organs and continue to grow, forming metastatic tumors. Various malignant tumors may occur, especially sarcoma, renal cancer, liver cancer, thyroid follicular carcinoma and choriocarcinoma. Tumor cells often enter the blood directly through capillaries and small veins (with thinner walls); they can also enter the blood through the lymphatic vessels-thoracic duct or through the lymphatic-venous pathway. Tumor cells that enter the vascular system often aggregate with fibrin and platelets into clumps called tumor embolus, which can be retained in the small blood vessels of the target organs, thereby mediating the degeneration of endothelial cells. Tumor cells can pass through blood vessels from endothelial damage or between endothelial cells, enter tissues, proliferate, and form metastatic tumors. The route of hematogenous metastasis is the same as that of emboli, that is, tumor cells that enter the systemic circulation veins travel through the right heart to the lungs, forming metastases in the lungs, such as lung metastasis of choriocarcinoma; tumor cells that invade the portal venous system first metastasize to the liver, such as liver metastasis of gastric and intestinal cancer; tumor cells that enter the pulmonary veins or tumor cells of lung metastases that enter the pulmonary veins through the pulmonary capillaries can reach various organs throughout the body through the left heart with the aortic blood flow, and commonly metastasize to the brain, bones, kidneys, and adrenal glands; tumor cells that invade the veins that have anastomoses with the vertebral venous plexus can cause metastases to the spine and brain. For example, spinal metastasis of prostate cancer.

Hematogenous metastases may occur in many organs, but the most common are the lungs, followed by the liver and bones. Therefore, clinically, patients with malignant tumors must undergo imaging examinations of the lungs, liver, and bones to determine whether they have blood metastasis in order to determine the clinical stage and treatment plan. The morphological characteristics of metastatic tumors are clear boundaries and often divergent distribution, mostly located on the surface of organs. Due to bleeding and necrosis in the center of the tumor nodule, it sinks and forms a "cancer navel."

(3) Transcoelomic metastasis: When tumor cells invade the surface of body cavity organs, they can fall off and implant on the surface of various organs in the body cavity or even invade and grow underneath them, forming metastatic tumors. For example, after gastric cancer destroys the gastric wall and invades the serosa, it may form extensive implant metastases on the surfaces of abdominal and pelvic organs. Ovarian Krukenberg tumors are mostly caused by gastric mucinous carcinoma implanting into the ovarian surface serosa through the abdominal cavity and then invading the ovary to form a tumor. Lung cancer often forms extensive implant metastases in the chest cavity. Malignant brain tumors, such as medulloblastoma of the cerebellum, can also metastasize to other parts of the brain through the cerebrospinal fluid, forming implanted metastases. Metastasis through the body cavity is often accompanied by body cavity effusion and cancerous adhesions between organs. The effusion is mostly bloody and contains detached cancer cells, which can be used for cytological examination. It is worth noting that surgery can also cause iatrogenic implantation, although the possibility is small, it should be avoided as much as possible.