Metastasis

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