A11. The routes of spread of malignant tumors
There are five routes of spread of malignant neoplasms:
- Direct extension
- Lymphatic spread
- Haematogenous spread
- Spread through serous cavities (intracavital)
- Intraluminal spread
Direct extension
Direct extension occurs when the cancer spreads directly into nearby organs.
Lymphatic spread
Lymphatic spread is most typical for carcinomas and is evidenced by spread to the sentinel lymph node.
Haematogenous spread
Haematogenous spread most commonly follows veins rather than arteries, due to their thinner, easier-to-invade walls. Typical examples include:
- Kidney cancer spread to the lung through IVC
- Colorectal cancer spread to the liver through the portal vein
- Lung cancer spread to the brain through the pulmonary veins
- Prostate cancer spread to the vertebrae through the vertebral venous plexus
Intracavital spread
Intracavital metastasis refers to the dissemination of malignant tumours into serous body cavities by penetrating the surface of the peritoneal, pleural, pericardial, or subarachnoid spaces. Of these, transperitoneal metastasis is the most common.
Ovarian tumours spread transperitonally most of the time, although they can also spready through the lymphatics or blood vessels. Ovarian metastasis to the liver is typical.
Intraluminal spread
Intraluminal spread refers to spread within one place of a hollow organ to another. This is very rare, but has been described for colorectal metastasis to the small bowel, for example.
Spread by iatrogenic implantation
Malignant tumours may spread during medical procedures used to diagnose or treat a malignancy; a process also called seeding. Preventing this is an important principle in the diagnosis and treatment of cancer. Here are some examples used to prevent this:
- During a laparoscopic tumour removal, the tumour is first put into a sample bag and then removed from the abdominal cavity
- After tumour removal, the abdominal cavity is often washed with distilled water, which causes lysis of any exfoliated tumour cells
- Needle biopsy and incisional biopsy are not performed for certain tumours, like HCC, breast cancer