page_title: Metastasis
section_title: Lymphatic spread
hierarchical_section_title: Metastasis / Pathophysiology / Routes / Lymphatic spread
caption_attribution_description: English: Lymph node with almost complete replacement by metastatic melanoma. The brown pigment is focal deposition of melanin. Author: Gabriel Caponetti, MD
context_page_description: Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then, are metastases. It is generally distinguished from cancer invasion, which is the direct extension and penetration by cancer cells into neighboring tissues.
  Cancer occurs after cells are genetically altered to proliferate rapidly and indefinitely. This uncontrolled proliferation by mitosis produces a primary heterogeneic tumour. The cells which constitute the tumor eventually undergo metaplasia, followed by dysplasia then anaplasia, resulting in a malignant phenotype. This malignancy allows for invasion into the circulation, followed by invasion to a second site for tumorigenesis.
  Some cancer cells known as circulating tumor cells acquire the ability to penetrate the walls of lymphatic or blood vessels, after which they are able to circulate through the bloodstream to other sites and tissues in the body. This process is known as lymphatic or hematogenous spread.
context_section_description: Lymphatic spread allows the transport of tumor cells to regional lymph nodes near the primary tumor and ultimately, to other parts of the body. This is called nodal involvement, positive nodes, or regional disease. "Positive nodes" is a term that would be used by medical specialists to describe regional lymph nodes that tested positive for malignancy. It is common medical practice to test by biopsy at least one lymph node near a tumor site when carrying out surgery to examine or remove a tumor. This lymph node is then called a sentinel lymph node.
  Lymphatic spread is the most common route of initial metastasis for carcinomas. In contrast, it is uncommon for a sarcoma to metastasize via this route. Localized spread to regional lymph nodes near the primary tumor is not normally counted as a metastasis, although this is a sign of a worse outcome. 
  The lymphatic system does eventually drain from the thoracic duct and right lymphatic duct into the systemic venous system at the venous angle and into the brachiocephalic veins, and therefore these metastatic cells can also eventually spread through the haematogenous route.
caption: Lymph node with almost complete replacement by metastatic melanoma. The brown pigment is focal deposition of melanin
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