- A tumor which has spread to areas of the body distant or remote from the primary tumor.
- Distant metastases are comprised of tumor cells which have broken away from the primary tumor and have traveled to other parts of the body.
- Also called remote, disseminated, diffuse, metastatic.
Methods of Spread:
- Extension from primary organ beyond adjacent tissue into next organ. Example: lung to pleura or lung to bone (rib).
- Travel in lymph channels beyond the first drainage area. Tumor cells can be filtered, trapped and grown in any lymph nodes in the body.
- Hematogenous or blood-borne metastases. Invasion of blood vessels within the primary tumor (veins are more susceptible to invasion than thicker-walled arteries) allows escape of tumor cells or tumor emboli which are transported through the blood stream to another part of the body where it lodges in a capillary or arteriole. At that point the tumor penetrates the vessel wall and grows back into the surrounding tissue.
- Spread through fluids in a body cavity. Example: malignant cells released into the thoracic or peritoneal cavity float in the fluid and can land on and begin to grow on any tissue reached by the fluid. Also called: implantation or seeding metastases. Forms large quantities of fluid which can be removed but rapidly re-accumulate. Note: The presence of fluid or ascites does not automatically indicate dissemination there must be cytologic evidence of malignant cells.
Common Sites of Spread:
Common sites of spread are liver, lung, brain, bones. These organs receive blood flow from all parts of the body. However, if the primary site is adjacent, review staging scheme for that site to make sure the disease is not a regional extension. (Example: Liver involvement from primary in gallbladder may be regional by direct extension, since the gallbladder is adjacent to the liver.)
Guidelines for Staging Distant Disease:
- If distant metastases are recorded on x-ray or needle biopsy, the stage is already determined and the patient does not need to be put through a lot of other tests.
- Hematopoietic diseases (leukemia and myeloma) are considered disseminated at time of diagnosis.
- In recording extent of disease, not whether there is a lymphatic or vascular invasion and/or spread, which organs are involved, whether there is a single focus or multiple foci of tumor.
- Terms such as "blood vessel invasion" or "perineural lymphatic invasion" should not be the sole basis for staging a tumor as distant.
- If tumor at primary has invaded lymph or blood vessels, there is the potential for malignant cells to be transported throughout the body. Step 1 (invasion) has occurred, but steps 2 (transport) and 3 (growth) may not.
- Vascular invasion within the primary is not a determining factor in changing the stage unless there is definite evidence of tumor at distant sites.