Lentigo maligna melanoma, primary

**Definition:** Lentigo maligna malignant melanoma is a form of melanoma which occurs within a lentigo maligna when neoplastic cells no longer remain confined to the epidermis (in situ radial growth) but invade the dermis (vertical growth). The lentigo maligna from which it arises may have been present as an irregularly pigmented macule on sun-exposed skin for many years before dermal invasion supervenes. Clinical differentiation from lentigo maligna may not be possible in the early stages of invasion but as the tumour progresses a focal thickening or nodule within the lentigo maligna will become apparent.

**Exclusions:** - Lentigo maligna