This article was last reviewed and updated on June 13, 2019
by Robyn Ndikumana MD BScN and Allison Osmond, MD FRCPC
Lentigo maligna is an early form of non-invasive skin cancer and a type of melanoma.
Unlike other types of melanoma, the cancer cells in lentigo maligna have not spread beyond the surface of the skin.
It develops in sun damaged skin and is most common on the head and neck.
Skin is made up of three layers: epidermis, dermis, and subcutaneous fat. The surface and the part you can see when you look at your skin is called the epidermis. The cells that make up the epidermis include: squamous cells, basal cells, melanocytes, Merkel cells, and cells of the immune system. The squamous cells in the epidermis produce a material called keratin which makes the skin waterproof and strong and protects us from toxins and injuries.
The dermis is directly below the epidermis. The dermis is separated from the epidermis by a thin layer of tissue called the basement membrane. The dermis contains blood vessels and nerves. Below the dermis is a layer of fat called subcutaneous adipose tissue.
Melanocytes are small cells that produce melanin, a dark pigment that helps protect our skin from the sun’s ultraviolet rays.
The amount of melanin normally found in our skin determines our skin colour. People with very light skin produce very little melanin while people with very dark skin produce a lot of melanin.
What is lentigo melanoma?
Lentigo maligna is a type of early, non-invasive skin cancer made up of melanocytes. Another name for lentigo maligna is melanoma in-situ. In lentigo maligna, the abnormal melanocytes are only found in the top layer of the skin called the epidermis.
The melanocytes in lentigo maligna are larger and darker than normal melanocytes and they grow in groups or in between the keratinocytes in the epidermis. If these abnormal melanocytes move beyond the epidermis into the dermis or subcutaneous tissue the diagnosis changes to malignant melanoma. The movement of tumour cells from the epidermis into the dermis is called invasion.
Without a microscope, lentigo maligna can look like a dark brown or black growth on the skin. The growth usually has an irregular shape and it may be difficult to see where the growth ends and the normal skin begins (the border).
Unfortunately, lentigo maligna and malignant melanoma can look the same without a microscope. The only way to tell the difference between these two conditions is for your doctor to remove a small sample of tissue in a procedure called a biopsy. Your pathologist will then examine the tissue under the microscope and make a diagnosis.
Your pathologist will also decide if the abnormal tissue has been fully removed. If all of the abnormal tissue has been removed, your report will say that the margins are negative. In contrast, a positive margin or “incompletely excised” means that some of the abnormal tissue has been left in your body. In that case your doctor will probably suggest another surgical procedure to remove the rest of the abnormal tissue.
If the area of lentigo maligna involves a large area of skin, you may be offered a cream called Imiquimod (Aldera). This is particularly useful for cosmetically sensitive areas like the face.