Types and Stages of Melanoma

Melanoma is not one single disease. It is a family of cancers. All of them start in melanocytes, the cells that give skin its color. Most melanomas start in the skin. A few start in other places. This includes the eye, or the lining inside the nose or mouth. Knowing the type helps explain where to look. It also explains how fast a melanoma tends to grow. And it explains why some melanomas get caught late, even with careful skin checks.

About 7 in 10 skin melanomas are superficial spreading melanoma. It usually grows outward across the surface of the skin first, before it grows deeper. This slower, sideways growth pattern helps it get caught early. It is often found while still thin and highly treatable. It can develop from an existing mole. It can also appear as a new spot that slowly expands and darkens.

Nodular melanoma makes up about 2 in 10 skin melanomas. It does not spread across the surface first. It grows downward into the skin from the start. It shows up as a firm, raised bump, usually dark but sometimes pink or red. It skips the slow surface-spreading phase. Because of that, it is more often found at a deeper, more advanced stage. A new, raised, fast-growing bump deserves prompt attention. This is true even if it does not look like the classic dark, flat mole.

Lentigo maligna melanoma mainly affects older adults. It usually appears on skin with years of sun exposure, like the face. It often starts as an unevenly shaped tan or brown patch. It grows very slowly, sometimes over many years, before becoming invasive. Its slow pace gives a real window for catching it early. That only works if the patch gets checked, instead of being dismissed as an age spot.

Acral lentiginous melanoma grows in places sun exposure does not reach. This includes the palms, the soles of the feet, and under the nails. It is not linked to sun exposure the way other types are. This is the most common type of melanoma in people with darker skin tones. It is often diagnosed later. Part of the reason is that it shows up in places people and doctors check less often. A dark streak under a nail, not caused by injury, should be evaluated. So should a new dark patch on a palm or sole.

A small number of melanomas start somewhere other than the skin entirely. Ocular melanoma develops inside the eye. It most often starts in a layer called the uvea. It may cause no symptoms and can be found during a routine eye exam. Mucosal melanoma starts in moist lining tissue. This includes the nose, mouth, throat, and the genital or anal area. Both types are far less common than skin melanoma. Because they are hidden from view, they are often found later than skin melanomas are.

Type tells you what a melanoma is. Stage tells you how far it has gone. NCI's patient summary numbers the stages 0 through IV.

• Stage 0. Abnormal melanocytes sit in the epidermis, the top layer of skin. They may become cancer and spread into nearby normal tissue.
• Stage I. Cancer has formed, and the tumor is no more than 2 millimeters thick.
• Stage II. The tumor is thicker, up to 4 millimeters, and grouped by thickness and by whether the surface is broken.
• Stage III. The melanoma has reached nearby lymph nodes or the skin and tissue around the original spot.
• Stage IV. The melanoma has spread to distant sites, such as lung, liver, brain, bone, soft tissue, or distant lymph nodes.

Two features drive the early stages. One is thickness, measured from the surface of the skin down to the deepest part of the tumor. The other is ulceration, meaning the skin over the melanoma is broken.

To work the stage out, the tumor is removed and measured under a microscope. Nearby lymph nodes may be checked, often with a sentinel lymph node biopsy, and imaging may be used to look further afield.

The ABCDE rule helps evaluate a spot. A is for asymmetry, where one half does not match the other. B is for a border that is irregular or blurred. C is for color that varies within one spot. D is for diameter larger than about 6 millimeters, the size of a pencil eraser — though smaller melanomas do exist. E is for evolving, meaning the spot is changing. Doctors also use the "ugly duckling" sign alongside ABCDE. A spot that simply looks different from all your other spots is worth a second look, even if it does not clearly break any single ABCDE rule.

• Which type of melanoma do I have, and how does that affect how it is monitored or treated?
• Should my palms, soles, nails, and scalp be checked, not just sun-exposed skin?
• How often should I have a full skin exam, given my history?
• If a spot changes between visits, how quickly should I be seen?

• American Cancer Society — What Is Melanoma Skin Cancer?
• American Cancer Society — Signs and Symptoms of Melanoma Skin Cancer