Skin cancer is a broad term that refers to any type of cancer that begins in the cells of the skin. These cancers usually develop in the top layer of skin, also known as the epidermis.
The most common types of skin cancer are basal cell carcinoma, squamous cell carcinoma and melanoma. In addition, there are several types of skin cancers that occur much less frequently, including kaposi sarcoma, merkel cell carcinoma, cutaneous (skin) lymphoma, skin adnexal tumors and various types of sarcomas.
Each year, more 2 million cases of skin cancer are diagnosed in the United States, and the incidence is increasing.
Skin cancer may initially appear as a bump, nodule or irregular patch on the surface of the skin. As the cancer grows, the size or shape of the visible skin mass may change. As these visible changes are occurring, the cancer is likely expanding and moving into the lower layers of the skin.
If left untreated, skin cancer will continue to grow down into the dermis and the subcutaneous tissues. In the most advanced stages, skin cancer may spread into nearby muscle tissue, cartilage or bone. Once the cancer spreads into the blood or lymph fluids, it may reach other areas in the body, like the liver or lungs.
Melanoma: These cancers develop within specialized cells called melanocytes that produce the skin pigment, melanin. A collection of melanocytes may form a mole, a type of benign (non-cancerous) growth. Most moles never develop into cancer, but a mole that begins to change in size, shape or color may be a sign of melanoma. Melanoma is highly curable if caught early, but is much more likely than other types of skin cancer to spread if left untreated. Melanoma accounts for approximately 5 percent of all skin cancers.
Basal Cell Carcinoma: According to the American Cancer Society, basal cell carcinomas are the most common type of skin cancer, and approximately eight out of every 10 non-melanoma skin cancers will be basal cell carcinoma. These cancers develop within the basal cell layer of the skin - the lowest part of the epidermis. This type of skin cancer tends to occur in areas of the skin that receive the most exposure to the sun, like the head and neck. Basal cell cancers usually grow slowly, and it is rare for them to spread, or metastasize, to nearby lymph nodes or even more distant parts of the body. However, this can occur if the cancer is left untreated, so early detection and treatment is important.
Squamous Cell Carcinoma: These cancers are the second most common type of skin cancer, accounting for approximately 20 percent of non-melanoma skin cancers. They develop from the flat, squamous cells that are the primary cell type making up the outermost layer of the skin, the epidermis. This type of skin cancer is usually found on areas of the skin that have been exposed to the sun, such as the neck or ears, face, or on the back of the hand, but they can develop in other areas, such as in scars or skin ulcers, or in the genital region. Squamous cell cancers usually grow slowly, and it is uncommon for them to spread, or metastasize, but they are more likely than basal cell carcinomas to invade fatty tissue beneath the skin or to spread even further.
Keratoacanthoma: These tumors are usually benign (non-cancerous), slow growing and often go away on their own. Keratoacanthomas tumors that do continue to grow are often treated like a form of squamous cell carcinoma.