Routes of spread
Cancer has different ways of spreading. It is worth saying here that there is a difference between metastasis and direct invasion. Metastases have to be isolated from the main tumor.
Types of spread include:
- Lymphatic spread: This is the case with most cancers of the carcinoma type and generally the most common way of spread of cancers. Cancer cells first affect a lymph node called the sentinel lymph node, then spread to the others. Lymph nodes are affected in a retrograde manner, which means that groups are affected one after another until reaching the end of the lymphatic system backwards. Since lymph nodes drain specific areas called “territories”, it is possible to locate the main tumor by examining the territory of the affected lymph node.
- Hematogenous (blood) spread: Hematogenous spread is the end stage of lymphatic spread and is the most common route in case of a type of cancers called sarcoma. It is generally more dangerous than lymphatic spread.
- Transcoelemic spread: This way of spread is related to body cavities. The abdomen is lined by a special tissue called the peritoneum and the chests by the pleura. Cancer cells “creep” along those linings to affect other organs within the same cavity. This is commonly seen in case of ovarian cancer that may affect the stomach.
- Perineural spread: This is a rare method that involves spreading of cancer along the nerve fibers. It is seen in some types of parotid gland cancers which may reach the brain via the facial nerve that passes through the gland.
- Canalicular spread: This way of spread is often underestimated and underdiagnosed. It involves the spread of cancer along natural “tubular structures” to reach another organ or another part of the same organ. This can be seen in cases of lung cancer, when the cancer cells move along the airways. Another example can be found in cancers of the bile ductal system.