Computed tomography (CT) scan of an axial section through the chest of a 77 year old man with metastatic melanoma. A secondary tumour is seen in the lymph nodes of the left armpit (at right here). Melanomas are invasive cancers, and may spread to other parts of the body (metastasis). If this occurs, the prognosis is poor. This patient's primary cancer was on the neck. Melanomas are the most dangerous form of skin cancer. The lymph nodes and other glands are commonly affected by cancer as it spreads from its primary site.