Introduction Spread of a neoplasm to distant tissues Cellular requirements invasive carcinoma progression that reaches a blood or lymph vessel increased angiogenesis at metastatic foci decreased adhesion to fibronectin, collagen, and laminin ability to survive in distant tissue May spread hematogenously or via lymphatics sarcomas most commonly spread via blood carcinomas most commonly spread via lymphatics most notable exceptions include renal cell carcinomas, follicular carcinomas of the thyroid, and hepatocellular carcinoma all prefer hematogenous spread If neoplasm is multifocal and well-circumscribed, strongly consider metastasis multiple independent cancers are rare Most common sites of metastasis include lung liver metastasis much more common than primary tumors brain metastasis equivalent in frequency to primary tumors bone metastasis much more common than primary tumors lymph nodes are the most common site of metastasis These organs receive a large proportion of blood supply making metastatic seeding more likely in these areas Metastasis to brain Due to blood flow patterns and masses normally present at gray-white border Primary tumors that metastasize to brain include lung > breast > skin (melanoma) > kidney (renal cell carcinoma) > GI pulmonary circulation immediately enters the brain once leaving left heart Metastasis to liver The liver and lung are the most common sites of metastasis after the regional lymph nodes Primary tumors that metastasize to the liver include colon > stomach > pancreas > breast > lung colon drained by portal vein which empties into liver Metastasis to bone Primary tumors that metastasize to the bone include prostate = breast > thyroid > testes > lung > kidney vertebrae seeded by Batson's venous plexus Metastasis to bone may be bone forming (blastic) or bone destructive (lytic) lung = lytic presents with hypercalcemia prostate = blastic presents with high alkaline phosphatase breast = both lytic and blastic