Section Editor: Allison Osmond MD FRCPC
June 11, 2026
Lentigo maligna melanoma is a type of melanoma, a skin cancer that develops from melanocytes, the pigment-producing cells of the skin. It arises in skin with heavy long-term sun damage, such as the face, neck, and arms, and it usually affects older adults with lighter skin. It begins as a noninvasive cancer called lentigo maligna, which is confined to the top layer of the skin (the epidermis). When the cancer cells grow down into the deeper layer of the skin (the dermis), the diagnosis becomes lentigo maligna melanoma.
This article explains what a diagnosis of lentigo maligna melanoma means, what the findings in your pathology report describe, and how those findings guide the decisions you and your care team make together. Lentigo maligna melanoma usually grows slowly, and tumors that are found early and are still thin generally have a very good outlook.
What causes lentigo maligna melanoma?
Lentigo maligna melanoma is caused by long-term, excessive exposure to ultraviolet (UV) light, usually from the sun. Over many years, UV light damages the DNA in melanocytes, leading to numerous genetic changes (mutations). People with light skin who sunburn easily and tan poorly are at greater risk. Lentigo maligna sometimes appears next to solar lentigines (sunspots), although it is not clear whether these spots are true precursors or simply happen to occur in the same sun-damaged skin.
What are the symptoms of lentigo maligna melanoma?
Lentigo maligna melanoma usually starts as a flat or slightly raised patch on sun-damaged skin that changes slowly over time. Helpful warning features can be remembered as the “ABCDEs”:
- Asymmetry — One half of the spot looks different from the other.
- Border irregularity — The edges are uneven or poorly defined.
- Color variation — The spot may show more than one color, including shades of brown, black, gray, red, or skin tones.
- Diameter — It grows larger over time, often more than 6 millimeters across.
- Evolution — It changes in size, shape, or color.
Sometimes the tumor lacks pigment and appears pink or red (amelanotic), which can make it look like an inflamed patch of skin. More advanced tumors may develop a raised area, a nodule, or an open sore (ulcer) that can bleed; these changes can signal deeper growth into the skin.
How is the diagnosis made?
The diagnosis is made after a biopsy, in which a sample of the suspicious area is removed and examined under the microscope by a pathologist. Before the biopsy, a doctor may use a dermatoscope, a tool that magnifies the skin, to look for subtle features. Under the microscope, the pathologist looks for abnormal melanocytes extending into the dermis, which distinguishes invasive lentigo maligna melanoma from the noninvasive lentigo maligna from which it arises.
The melanocytes in lentigo maligna melanoma appear abnormal, with cells that vary in size and shape, and they spread along the bottom of a thinned epidermis, often extending into hair follicles and sweat gland openings. The invasive part of the tumor extends into the dermis and may consist of spindle-shaped (spindle cell) or desmoplastic (scar-like) melanocytes. Severe solar elastosis, a type of sun damage to the connective tissue of the dermis, is always present, and in some cases can resemble other pigmented spots such as a dysplastic nevus. Because the changes can be subtle, the pathologist often uses immunohistochemistry (special stains that detect specific proteins in the cells) to highlight the melanocytes and show how far they extend. Stains such as S100, Melan-A, and SOX10 mark melanocytes, and a stain called PRAME can help confirm melanoma and judge whether the lesion reaches the edges of the sample. Once invasive melanoma is confirmed, imaging may be used to check for spread and to help determine the stage.
Tumor thickness
Lentigo maligna melanoma starts in the epidermis and, as it grows, spreads into the deeper layers below, including the dermis and the fatty tissue beneath it. This downward growth is called invasion. Tumor thickness, also called Breslow thickness, is the distance from the surface of the skin to the deepest tumor cell, measured in millimeters. It is one of the most important numbers in the report because it determines the tumor stage (pT) and because thicker tumors are more likely to spread to other parts of the body, such as the lymph nodes and the lungs.
Ulceration
An ulcer is a break in the skin’s surface where the top layer of cells has been lost. For a melanoma, ulceration means the epidermis over the tumor has broken down. Ulceration is important because ulcerated tumors tend to behave less favorably, and its presence raises the tumor stage (pT).
Mitotic rate
A mitotic figure is a cell in the process of dividing into two new cells. The pathologist counts the number of these dividing cells in a set area of tumor (usually 1 square millimeter), and this count is called the mitotic rate. The mitotic rate is recorded because tumors that divide more quickly are more likely to spread, so it provides useful prognostic information even though it is no longer used to assign the tumor stage.
Tumor-infiltrating lymphocytes (TILs)
Tumor-infiltrating lymphocytes are immune cells called lymphocytes that surround or move into the tumor. They are a sign that the immune system is responding to the cancer, and in melanoma, a stronger response is generally associated with a better outcome. The report usually describes them in one of three ways: none identified, non-brisk (few lymphocytes), or brisk (many lymphocytes).
Tumor regression
Tumor regression is the partial or complete disappearance of tumor cells from an area where they were previously present. The tumor cells are replaced by immune cells or scar tissue (fibrosis), thought to occur when the immune system attacks and destroys the tumor. Regression can make it harder to measure the true thickness of the tumor, which is why the pathologist notes it.
Microsatellites
A microsatellite is a small group of tumor cells that has spread from the main tumor into nearby skin, separate from the main mass. This is a form of local metastasis. Microsatellites are important because they indicate that the tumor has begun to spread and raise the pathologic nodal stage (pN).
Lymphovascular invasion
Lymphovascular invasion means that tumor cells are seen inside a blood vessel or a lymphatic channel. Blood vessels carry blood, while lymphatic channels carry a clear fluid called lymph and connect to the lymph nodes. These vessels give tumor cells a route to spread to lymph nodes or distant organs such as the lungs, so the presence of lymphovascular invasion is associated with a higher risk of spread. Your report will state whether it was seen.
Perineural invasion (neurotropism)
Perineural invasion, also called neurotropism, means that tumor cells are attached to or growing along a nerve. Nerves carry signals such as temperature, pressure, and pain between the body and the brain. Perineural invasion is important because tumor cells can travel along a nerve into surrounding tissue, which raises the risk that the tumor will come back after surgery. It is more common in the desmoplastic form of lentigo maligna melanoma. Your report will state whether it is present.
Surgical margins
A margin is the edge of the tissue removed during surgery. The margin status tells you and your doctor whether the whole tumor was removed or whether some may have been left behind.
- Negative margin — No tumor cells are seen at the cut edge, which suggests the tumor was completely removed. The pathologist often also measures the distance from the nearest tumor cells to the edge.
- Close margin — Tumor cells are near the cut edge but do not reach it. Depending on the distance, more surgery may be considered.
- Positive margin — Tumor cells are present at the cut edge, which means some tumor may remain. A positive margin may lead to further surgery or radiation. Lentigo maligna melanoma can be especially difficult to remove completely because the in situ part of the tumor often extends well beyond what is visible to the eye.
Lymph nodes
Lymph nodes are small immune organs found throughout the body that filter lymph and help fight infection. Melanoma cells can travel through lymphatic channels to reach the lymph nodes near the tumor; when tumor cells are found in a node, this is called a metastasis. The sentinel lymph node is the first node to receive drainage from the tumor and is usually the first site where melanoma spreads, so it is often sampled to detect microscopic disease. Nodes farther away (non-sentinel nodes) are usually involved only after the sentinel node.
If lymph nodes are removed, the report describes the total number of nodes examined, their locations, how many contain tumor, and the size of the largest deposit. The report may also note extranodal extension, meaning tumor cells have broken through the thin capsule surrounding a lymph node into the surrounding tissue. Extranodal extension is important because it raises the risk that the cancer will come back in that area and may influence decisions about additional treatment. Lymph node findings are used to determine the pathologic nodal stage (pN).
Biomarker and molecular testing
Biomarkers are features of the tumor, usually genes or proteins, that provide information beyond the diagnosis itself, such as how the cancer may behave and which treatments may help. In melanoma, the most useful biomarkers are genetic changes that can open the door to targeted therapy. These are usually tested by genetic methods such as next-generation sequencing (NGS) and are most relevant when the melanoma is thick, has spread, or has come back.
BRAF
BRAF is a gene that helps control cell growth. The report describes the result in one of two ways:
- Positive (mutation detected) — A change in the BRAF gene, most often called V600E, is present. About half of all melanomas carry a BRAF mutation. A positive result makes the tumor eligible for targeted therapy with BRAF inhibitors (such as vemurafenib or dabrafenib), usually combined with MEK inhibitors.
- Negative (no mutation detected) — No BRAF mutation is found. BRAF-targeted therapy is not used in this situation, but other treatments, including immunotherapy, remain available.
NRAS
NRAS is another gene involved in cell growth. The report states whether an NRAS mutation is present and, if so, which one. NRAS mutations are found in about 20% of melanomas and usually do not occur together with a BRAF mutation. There is no approved targeted therapy specifically for NRAS, but a positive result suggests a different tumor biology and may influence treatment planning, including the use of immunotherapy and eligibility for clinical trials. A negative result means no NRAS mutation was found.
KIT
KIT is a gene that helps regulate cell growth and survival. KIT mutations are found in fewer than 5% of melanomas, most often in melanomas arising in chronically sun-damaged skin (the setting of lentigo maligna melanoma) and in acral and mucosal melanomas. The report states whether a KIT mutation is present and, if so, the specific type. A positive result may indicate that the tumor is responsive to targeted therapy with a tyrosine kinase inhibitor such as imatinib; a negative result means no KIT mutation was found.
Importantly, immunotherapy (treatment that helps the immune system attack the cancer) is a mainstay of treatment for advanced melanoma and is used based on the diagnosis and stage rather than on a single biomarker test. You can read more in the Biomarkers section of this site.
Pathologic stage (pTNM)
The pathologic stage describes how advanced the cancer is, based on the tissue removed at surgery. Melanoma is staged using the TNM system of the AJCC (American Joint Committee on Cancer), 8th edition, which combines the thickness and ulceration of the tumor (T), spread to lymph nodes or nearby skin (N), and spread to distant organs (M). The M category is determined by imaging and blood tests rather than by the pathologist. Higher numbers indicate more advanced disease.
Tumor stage (pT)
- Tis — Melanoma in situ; the cancer is confined to the epidermis and has not invaded deeper layers.
- pT1 — Tumor is 1 mm thick or less. pT1a: less than 0.8 mm without ulceration. pT1b: less than 0.8 mm with ulceration, or 0.8 to 1.0 mm with or without ulceration.
- pT2 — Tumor is more than 1 mm but no more than 2 mm thick (pT2a without ulceration, pT2b with ulceration).
- pT3 — Tumor is more than 2 mm but no more than 4 mm thick (pT3a without ulceration, pT3b with ulceration).
- pT4 — Tumor is more than 4 mm thick (pT4a without ulceration, pT4b with ulceration).
Nodal stage (pN)
- pN0 — No tumor is found in nearby lymph nodes and no microsatellite, satellite, or in-transit deposits are present in nearby skin.
- pN1 — Tumor in one lymph node, or tumor in nearby skin (microsatellite, satellite, or in-transit) without lymph node involvement.
- pN2 — Tumor in two or three lymph nodes, or in one lymph node together with tumor in nearby skin.
- pN3 — Tumor in four or more lymph nodes, in matted (clumped) nodes, or in two or more nodes together with tumor in nearby skin.
- pNX — The lymph nodes could not be assessed.
What is the prognosis?
The outlook for lentigo maligna melanoma is similar to that of other melanomas of the same thickness, and because it tends to grow slowly and is often found while still thin or in situ, many people have an excellent outlook. As a general guide, melanoma that is still limited to the skin has a five-year survival of roughly 95% or higher when thin, while melanoma that has spread to regional lymph nodes or distant organs has a lower survival. Immunotherapy and targeted therapy have substantially improved outcomes for advanced disease in recent years. The most important factors are how thick the tumor is and whether it has spread.
Features in the pathology report associated with a higher risk that the cancer will spread or come back include:
- Greater tumor thickness — Thicker tumors are more likely to spread.
- Ulceration — Breakdown of the skin surface over the tumor.
- Higher mitotic rate — More rapidly dividing tumor cells.
- Lymphovascular or perineural invasion — Tumor in vessels or along nerves.
- Microsatellites or lymph node involvement — Signs that the tumor has begun to spread.
What happens after this diagnosis?
Treatment is usually coordinated by a team that may include a dermatologist, a surgeon, a radiation oncologist, a medical oncologist, and a pathologist. The main treatment for lentigo maligna melanoma is surgery to remove the tumor with a margin of normal skin; the width of the margin depends on the thickness of the tumor. Because the in situ part of the tumor often extends beyond what is visible, techniques that carefully check the edges, such as staged excision or Mohs micrographic surgery, are sometimes used on the face. For tumors thicker than a certain threshold or with higher-risk features, a sentinel lymph node biopsy may be offered to assess for microscopic spread.
When melanoma has spread, or when the risk of spread is high, the medical oncology team may consider immunotherapy with immune checkpoint inhibitors, which has become a mainstay of treatment for advanced melanoma, and, when a BRAF (or in some cases KIT) mutation is present, targeted therapy. Radiation therapy is used in selected situations, and for people who cannot have surgery, lentigo maligna (the in situ form) is sometimes treated with radiation or with a topical immune-activating cream. After treatment, regular skin and lymph node examinations are important, both to watch for recurrence and because people who have had one melanoma are at higher risk of developing another. Protecting the skin from further sun damage is an important part of long-term care.
Questions to ask your doctor
- How thick was my melanoma (the Breslow thickness), and what tumor stage was it?
- Was ulceration present?
- Was the tumor completely removed, or were the margins positive?
- If the margins were positive, do I need more surgery or radiation?
- Was lymphovascular or perineural invasion seen?
- Should I have a sentinel lymph node biopsy?
- Was my tumor tested for BRAF, NRAS, or KIT mutations, and what were the results?
- What is the stage of my melanoma, and what does it mean for my treatment?
- Would immunotherapy or targeted therapy be considered in my case?
- How often should I have follow-up skin and lymph node checks?
- Am I at higher risk of developing another melanoma?
- What can I do to protect my skin from further sun damage?
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