Modes of Spread 4m – Histopathology.guru

Metastasis is spread of tumor by implantation of tumor cells at different sites which is discontinuous with the primary tumor
It is an important feature of malignant tumors. Benign tumors never metastasize

This is common pathway for the dissemination of carcinomas (rarely sarcomas also). Eg. Breast carcinoma, colonic carcinoma.
Tumors does not contain functional lymphatics but the lymphatic vessels located at the periphery are sufficient to cause lymphatic spread.
Pattern of lymph node involvement follows the natural routes of lymphatic drainage
In some cases local lymphnodes may be bypassed (Skip metastasis) because of venous lymphatic anastomoses or because of inflammation or radiation obliterating lymphatic channels.
“Sentinel lymph node” biopsy is often used to assess presence or absence of metastasis to lymph nodes
Sentinel lymph node is defined as the first node in a regional lymphatic basin that receives the lymph flow from primary tumor
Sentinel lymph node mapping can be done by injecting radiolabeled tracers and blue dyes. Frozen section is done and lymph node status is examined to give the opinion to surgeon during surgery.
Lymph nodes may also act as barrier for tumor spread for minimum time as tumor cells may be destroyed by tumor specific immune response
Draining nodes may be enlarged due to

This is common mode of spread by sarcomas (also by carcinomas). Eg Leiomyosarcoma, fibrosarcoma
Arteries have thicker wall than veins and hence hematogenous spread occurs through veins.
Arterial spread occurs when tumor cells pass through pulmonary capillary bed or pulmonary arteriovenous shunts
In the venous invasion tumor cells come to rest at first capillary bed they come across
Commonly liver and lungs are involved, as the portal area drainage flows to liver and all the caval flows to the lungs.
Eg. Renal cell carcinoma always invades the renal vein and grows in the vein in a snake like fashion up to the inferior vena cava and sometimes reaching the right heart. Hepatocellular carcinomas often penetrate portal and hepatic veins.
Many tumors does not follow the vascular drainage like breast carcinoma preferentially spreads to bone, bronchogenic carcinoma spreads to adrenals and brain, and neuroblastomas spread to liver and bones. Conversely, skeletal muscles and the spleen despite having large blood circulation are rarely the sites of metastasis.

When the tumor penetrates the surface of the organ it leads to seeding of the cavities and surfaces.
Most commonly peritoneal cavity is involved.
Other cavities involved are pleural, pericardial, subarachnoid and joint spaces
This route is more common in ovarian tumors. Tumor cells are coated on the surface of abdominal viscera and on the peritoneal cavity without infiltrating the organs.
Other tumors like mucin secreting appendiceal tumors also spread on to the peritoneal surface. The peritoneal cavity is filled with gelatinous mucin and peritoneal surface shows tumor implants. This condition is called “Pseudomyxoma peritonei”

References

Robbins Pathologic Basis of Disease