Melanoma is a serious type of skin cancer. It starts in skin cells called melanocytes. Melanocytes are what give skin its color.
There are 3 main types of skin cancer. Basal cell carcinoma and squamous cell carcinoma are more common. Melanoma is a much less common. But melanoma is more likely to spread to other parts of the body.
About your skin
The skin is the largest organ of the body. Skin protects us from heat, sunlight, injury, and infection. It also stores water and fat, and produces vitamin D. The skin has 3 layers:
The outer layer called the epidermis
The middle layer called the dermis
The inner layer called the subcutis (subcutaneous)
The epidermis is made of flat cells called squamous cells. Round basal cells are under the squamous cells. The lower part of the epidermis also has pigment-producing cells called melanocytes. These cells darken the skin when exposed to the sun.
The dermis has blood vessels, lymphatic vessels, hair follicles, and glands. Some of these glands make sweat, which helps keep the body cool. Other glands make sebum. Sebum helps keep the skin from getting dry. Sweat and sebum reach the skin's surface through tiny openings called pores.
The subcutis and the lowest part of the dermis form a network of collagen and fat cells. This layer conserves heat and helps protect the body's organs from injury.
Where melanoma occurs
Melanoma can occur anywhere on the skin. Men usually get it on the part of the body between the shoulders and the hips called the trunk. They may also get it on their head or neck. Women usually get it on their arms and lower legs. Sometimes, melanoma may occur even on areas of the skin that are never exposed to sunlight. It may even occur in the eye, under a fingernail or toenail, or in the nose and sinuses, or in other parts of the body.
Types of melanoma
Melanoma starts when normal melanocytes become cancerous. When cancer cells are on the skin, the cancer is called cutaneous melanoma. Most of what we know about melanoma (its behavior, staging, and treatment) refers to cutaneous melanoma.
Cutaneous melanomas come in these types:
Superficial spreading. This is the most common form, making up about 70% of all cutaneous melanomas. These often grow along the skin for a long time before invading the skin more deeply. They often have irregular shapes and are several shades of brown or other colors, such as black, blue, or red.
Nodular. These are often black, dome-shaped lesions. They tend to grow vertically (into deeper skin layers - see below).
Acral lentiginous. These are found on the palms of your hands, soles of your feet, under a nail (subungual), or on mucous membranes, such as the mouth, rectum, or vagina (mucosal). This type makes up a larger portion of melanomas in people with naturally darker skin.
Lentigo maligna. Common in older people, these lesions are typically flat and large, spreading widely along the surface of the skin. They often begin as benign lesions on the face or other sun-exposed area.
Desmoplastic or neurotropic. These melanomas show up as small nodules on the skin, which are nonpigmented (light in color). They can travel and grow along nerves in the skin and can cause the development of fibrous tissue.
Amelanotic melanoma. These melanomas are often pink or flesh-colored. They are variants of the more common melanomas because they don’t make pigment. As a result, they can be mistaken for a pimple or other noncancerous growth.
Keeping an eye on moles
Sometimes groups of melanocytes make moles, also called nevi. Most people have some moles on their bodies. These moles are usually pink, tan, or brown. They can be flat or raised, and are usually round or oval. Most moles are on the chest or the upper part of the body.
Moles don't usually grow or change very much. Moles can fade in older adults. Most moles are not cancer (benign), and do not lead to cancer. Some abnormal moles, called dysplastic nevi, are an increased risk of melanoma. These should be checked regularly by a doctor.
How melanoma spreads
If melanoma grows at the site of the original tumor, it tends to grow in 1 of 2 ways:
Radial growth. This means the melanoma spreads horizontally along the top layers of your skin. Most melanomas start growing this way, but some may eventually grow into deeper layers of your skin.
Vertical growth. This means melanoma grows into deeper layers of skin. This kind of growth is more serious and may spread to other parts of the body. Nodular melanoma grows this way fairly quickly, but most others grow along the top layers of skin first for some time.
If left untreated, melanoma tends to spread to other parts of the body more quickly than most other types of skin cancer, which can make it more dangerous. This spread can be somewhat unpredictable. Melanoma tends to spread first to lymph nodes in the area of your original tumor. For example, if the tumor was on your leg, it may spread to lymph nodes in your groin area. But, sometimes, melanoma may spread to distant areas of your body, such as the liver, lungs, or brain, even if your lymph nodes have not been involved.