Routes of Tumour Spread

Expansion

• Local invasion: direct extension into adjacent tissue
• Lymphatic: the usual first route for carcinoma. Follows drainage in an orderly fashion, which is the basis of sentinel node biopsy and of nodal staging
• Haematogenous: the usual route for sarcoma, and later for carcinoma. Venous drainage predicts the site, so gut tumours go to liver via the portal vein and most others to lung
• Transcoelomic: across body cavities. Ovarian and gastric carcinoma seeding the peritoneum, giving ascites and a Krukenberg tumour when gastric cancer seeds the ovaries; mesothelioma in the pleura
• Perineural: along nerve sheaths. Characteristic of prostate, pancreatic and adenoid cystic carcinoma, and a cause of pain and of local recurrence
• Implantation: iatrogenic seeding along a biopsy or drain track

Common sites of metastasis: liver, lung, bone, brain and adrenal.

Bone metastases are usually lytic, except prostate which is characteristically sclerotic. The classic primaries are breast, bronchus, kidney, thyroid and prostate.

Batson’s vertebral venous plexus explains spinal metastases without lung deposits, since it is valveless and bypasses the pulmonary filter.