A lot of work has been done to try and find ways of predicting what will happen, and what the chances of a cure are, after a malignant melanoma has been removed. It has been discovered that looking at the melanoma under the microscope, after it has been removed, and carefully measuring its vertical height within the skin (in other words, measuring how thick it is) gives a good indication of what the outlook might be.

There are two main ways of measuring the thickness of a melanoma. The first method gives the melanoma a ‘Clarke’s level’. This notes how many layers of the skin are affected by the melanoma, and results range from 1 – 5, with 5 being the deepest. A later and more useful system measures in millimetres how deeply melanoma has burrowed into the skin. This is called the Breslow thickness. (These two systems are named after the pathologists who created them).

Melanomas that are less than 1.5 millimetres thick are called 'thin' melanomas. If a thin melanoma has been completely removed by surgery then 9 out of 10 people will be cured. About half of all malignant melanomas turn out to be 'thin'.

For melanomas thicker than 1.5millimetres (and where there is no evidence of spread to the nearby lymph glands or to other parts of the body) the chances of cure after complete removal are slightly less, with about 6 out 10 people being cured. About 4 out of every 10 melanomas are found to be in this deeper group.