8. HOW DOES MELANOMA SPREAD?

Cutaneous melanoma (melanoma originating in the skin) grows and spreads in two phases called the radial and vertical growth phases.  During the radial growth phase melanoma grows horizontally across the surface of the skin.  At this stage the melanoma is called in-situ and the cure rate is extremely high.  The vertical growth phase occurs when the melanoma invades deeper layers of skin.  At this point the melanoma becomes dangerous as it now has the ability to enter either the blood stream or lymphatic system and spread to distant parts of the body.        

The spread of melanoma through the blood stream is called hematogenous.  For hematogenous spread to take place, melanoma cells must break away from the original tumour, find their way through a blood vessel wall and into the blood stream.  From there the melanoma cells must travel through the blood stream, until they lodge in a blood vessel, are able to break through the blood vessel wall and then form a secondary tumour.  Given the above mentioned requirements it is likely that many melanoma cells will not survive the journey. 

Lymphogenous spread or the spread of melanoma by the lymphatic system occurs in much the same way as hematogenous.  In the case of lymphogenous the melanoma cells travel through the lymphatic system and lodge in lymph glands, which usually enlarge.  Once the melanoma cells lodge in the lymph glands they can spread to the vascular system.  

Melanoma has the ability to metastasis locally and/or to distant locations.  In instances of melanoma metastasis it is common for signs of spread to be present.  The signs of both local and distant spread are as follows:

a) Local Spread - Presence of satellite nodules

When melanoma spreads from the original primary through the local lymphatic system and into the surrounding skin cells, they form what are known as satellite nodules.  Satellite nodules are small deposits of melanoma cells spread around the original primary tumour. These present as palpable lumps usually in the vicinity of the original tumour. 

b) Distant spread - A swollen Lymph gland/s

Lymph glands are bean-shaped glands that form part of the lymphatic system.  The lymphatic system is a series of inter-connected vessels that stretches the length and width of the body. It is responsible for filtering lymph, housing and transporting lympocytes (white blood cells) around the body and various other duties.  Normally a swollen lymph gland occurs as a result of infection.  However in some instances, a swollen lymph gland/s may indicate a spread of melanoma via the lymphatic system (lymphogenous).  A swollen Lymph gland is often the first sign of a distant spread of melanoma, as the lymphatic system filters the melanoma cells out of the lymph fluid.