The term "melanoma" is given to any abnormal collection of melanin-pigmented cells whether in the skin, in the eye or elsewhere. Malignant melanomas embrace tumors of widely diversified histologic structure.
Malignant melanomas may occur in many situations; the skin, the mucous membrane and the eyes are the most common sites. Rarely the meninges, ovary, epididymis and gallbladder may be involved. As a rule, malignant melanomas arising on the skin originate in pigmented moles or nevi, although there are many authentic cases on record in which melanomas have started at the sites of puncture wounds and in the absence of any apparent congenital abnormality.
Rare origins of malignant melanomas are the blue nevus of Jadassohn and the Mongolian spot. The Mongolian spot is a bluish lesion found in the sacral region. These lesions contain melanin and are devoid of nevus cells. When malignancy develops it is of a sarcomatous nature. Another