Melanoma of the iris. Illustration of the eye of a patient with a melanoma, a type of malignant tumour (cancer). The melanoma (brown) is on the iris, the coloured muscular ring that surrounds the pupil of the eye. Pigment dispersion has occurred on the fibrovascular upper layer of the iris, the stroma. The cancer has arisen from cells that produce the pigment (melanin). Melanomas are invasive cancers, and may spread to other parts of the body (metastasis). If this occurs, the prognosis is poor. If the cancer has not spread, surgical removal may effect a cure. Melanomas also occur on the skin, and are the most dangerous form of skin cancer.