Malignant melanoma. Ophthalmoscope image of a malignant melanoma (cancer) on the choroid of a patient's eye. The melanoma is the dark mass at centre right. It is a cancer of melanin-producing cells in the choroid, the membrane that underlies the light-sensitive retina and supplies it with blood. 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.