Coincident with this decent, nevi become less active and, therefore, less capable of converting into a malignant lesion. The most active nevus is the junctional nevus. Lentigo maligna is the premalignant form of lentigo maligna melanoma. This is found on the face of elderly patients and is related to exposure to the sun. Once this lesion penetrates into the dermis, it is classified as a lentigo maligna melanoma.
Melanocytes produce melanin and are derived from neural crest cells.
Benign lesions tend to maintain a uniform appearance, while malignant melanomas tend to be asymmetric, have irregular borders, and often are associated with changes in color. This has been taught to medical students as the ABCs of melanoma. They occur more commonly in light skin individuals and darken with sun exposure. These lesions reflect melanocyte overactivity, not proliferation. They usually appear in childhood, are unaffected by sun exposure, and are associated with Peutz-Jeghers syndrome.