Melanoma is a highly aggressive form of skin cancer that has a tendency to metastasise. It accounts for around 80% of skin cancer related deaths.
Australia has the world's highest incidence of melanoma. In Western Australia, melanoma is the most common cancer diagnosed in the 15-39 year-old age group and the third most common cancer in men and women over 39 years of age. It is increasing in incidence by 3% per year. Currently, over 1,000 people die annually from the disease in Australia.
In its early stages, the 5 year survival rate of patients is greater than 90% following surgical excision of an in situ tumour. However, following metastasis of the tumour, the 5 year survival rate declines to 5-35%. Due to the correlation between metastasis and declining survival, research studies have attempted to identify potential metastasis as early as possible.
Melanoma can be characterised initially by its appearance: the lesion is asymmetrical in shape, the borders of the lesion are irregular, the lesion may have many colours and generally the melanoma has a diameter greater than 2mm – the ABCD rule.
Once a melanoma has started to grow, it can extend downward into the dermis of the skin and develop the ability to infiltrate the blood vessels. The melanoma cells in the blood can circulate in the body and attach to the surface of another organ. The cells group together to form what is known as a micrometastasis. This small group of cells is practically invisible to current diagnostic techniques, and can go undetected for years. It is when the cells start to invade the new organ and grow into a tumour, that the survival rate of the patient starts to decrease. This process is termed as tumour metastasis.