The staging of any cancer requires us to look at the primary tumour, the lymph nodes and to distant sites which may be involved. This methodology is summarised by the American Joint Committee on Cancer’s approach using the TNM (Tumour-Nodes-Metastases) system.
A few factors can be determined directly from the primary tumour (T in the TNM system)
Ulceration
Aggressive tumours grow quickly and can ulcerate the overlying skin.
Mitotic Index
A measure of the rate of increase of tumour cells. A mitosis is a malignant cell in division. The higher the mitotic index the worse the prognosis.
Age
Younger patients have a better prognosis than older patients.
Site
Tumours of the head/neck have a worse prognosis than tumours of the trunk which have a worse prognosis than tumours of the limbs.
Why?
Because the lymphatic capillaries have greater access to multiple regional lymph node groups via a rich network of lymphatic capillaries.
Sex
Males have a worse prognosis than females but the reason is not fully understood. Possibly because the back is the commonest site in males and developing melanomas may go unnoticed.