Identifying Skin Cancers and Melanoma

IDENTIFYING THE MOST COMMON TYPES OF SKIN CANCER

Your skin is your body’s largest organ and your immune system’s first line of defense against infection and injury. Its thin, outer layer is called the epidermis, with the dermis underneath it and the hypodermis (subcutaneous tissue) farther below. More skin cancers are diagnosed in the United States each year than all other types of cancer combined

Skin cancer can develop anywhere on the body and is most frequently found on the face, including the eyelids and outer lips; the head, including the tops of the ears; the neck; and the tops of the hands, as these areas usually receive the most exposure to ultraviolet (UV) rays from the sun and other sources.

The most common types of skin cancer are named for the cells in which they develop: basal cell carcinoma and squamous (SKWAY-mus) cell carcinoma. Melanoma is less common and forms in cells called melanocytes (see Melanoma Overview, page 3). Merkel cell carcinoma is among the many rare types, subtypes and variants of cancers that affect the skin.

Basal cell and squamous cell carcinomas behave very differently from melanoma, which is why they are often grouped together and referred to as non-melanoma skin cancers (NMSCs). Although most NMSCs are usually easily cured and rarely life-threatening, they can cause serious tissue damage, particularly to the face and head, if left untreated.

Basal cell carcinoma (BCC) is the most common form of skin cancer in the United States, with more than 20 subtypes and variants. It is most frequently diagnosed in Caucasians, but is also the most common type seen in Hispanic and Asian people. BCC forms in basal cells, which are round cells in the lower part of the epidermis, and begins when these cells become abnormal and grow out of control. BCC usually grows slowly and very rarely spreads beyond surrounding tissues. The most common site for BCC to occur is the nose.

Squamous cell carcinoma (SCC) is less common than BCC. It is sometimes called squamous cell carcinoma of the skin, cutaneous squamous cell carcinoma (CSCC) or squamous cell skin cancer to differentiate it from SCC that develops in other parts of the body. SCC is commonly found on more sun-exposed areas of the skin, such as the face, ears, neck, lips and backs of the hands. It can also develop on scarred or damaged skin.

SCC develops in squamous cells, which form the outermost part of the epidermis. Under a microscope, these thin, flat cells resemble fish scales. SCC is more likely to spread than BCC, but it usually remains local, meaning it is confined to tissues surrounding the original site. Regional SCC has spread to nearby lymph nodes, and metastatic SCC has spread to distant parts of the body.

There are several SCC subtypes and related forms. Actinic keratosis (ak-TIH-nik KAYR-uh-TOH-sis) is a common skin condition also referred to as sun spots or age spots. These slow-growing lesions are most likely to appear on the face, balding scalp, forearms and backs of hands. Actinic keratosis is considered a precancer because it sometimes progresses to become SCC.  Squamous cell skin cancer in situ (in SY-too), also called Bowen disease, is SCC in its very earliest form and involves only the superficial layer of skin. It grows very slowly, and without treatment, it may become SCC. Marjolin’s ulcer, which can be aggressive, is SCC that develops at the site of an old scar, burn or non-healing wound.

Merkel cell carcinoma (MCC) is very rare. It forms in oval-shaped cells located in the basal layer in the lower part of the epidermis. These neuroendocrine cells are thought to be receptors that help produce the sensation of light touch. MCC begins when these cells become abnormal and grow out of control, most often in the head and neck area as well as the trunk, arms and legs. Because MCC is highly aggressive, it grows rapidly and is likely to spread, first to nearby lymph nodes and then to distant areas. These may include skin and lymph nodes elsewhere in the body, the brain, lungs, bones and other organs. MCC may also be referred to as neuro-endocrine carcinoma of the skin.

Immunotherapy may be used to treat some types of skin cancers under certain conditions, such as when cancer is advanced and/or surgery isn’t possible. Having a non-melanoma skin cancer significantly increases your risk of developing another skin cancer, so follow-up care is very important after being diagnosed with any type of skin cancer. This includes regularly scheduled appointments with a dermatologist.

QUESTIONS FOR YOUR DOCTOR

• How deeply has the cancer grown into my skin, and how does that affect my prognosis?
• How do we determine how serious my skin cancer is?• How will my type of skin cancer be treated?

EDUCATE YOURSELF ABOUT THE BASICS OF MELANOMA

Melanoma is a cancer that starts in skin cells known as melanocytes, which produce melanin, the substance that colors the skin, hair and eyes. Damaged DNA can cause the melanocytes to grow abnormally. When melanocytes become malignant (cancerous), they are called melanoma.

Melanomas can develop anywhere on the skin, in the eyes and in mucosal linings, such as in the mouth, genitals and anal area. The neck and face are common sites for melanoma of the skin. Melanocytes may also form moles that can turn into melanoma. Other names for this cancer of the skin include cutaneous melanoma and malignant melanoma.

TYPES OF MELANOMA

Although melanoma is the rarest of the skin cancers, it is considered the most serious type. It can easily spread into deep layers of skin as well as to lymph nodes and other organs. The skin’s layers include the epidermis (outer layer), dermis (inner layer) and hypodermis (subcutaneous tissue). Melanoma typically develops in the epidermis, which contains melanocytes.

Cutaneous melanoma includes four types:

• Acral lentiginous melanoma is found on the palms of the hands, soles of the feet or under the nail bed.
• Lentigo maligna melanoma typically begins on the face, ears and arms that have been exposed to the sun for long periods of time.
• Nodular melanoma usually appears suddenly as a bump on the skin.
• Superficial spreading melanoma develops from an existing mole.

Other rare subtypes of melanoma of the skin include amelanotic, which often lacks pigmentation, and desmoplastic, which is found in older adults and is distinguished by the presence of certain cell types.

Ocular melanoma develops in the eye. No screening tests are available for the disease, but routine eye exams help doctors find most ocular melanomas. Because they do not typically cause symptoms in the early stages, melanomas that develop as a dark spot in visible parts of your eye (primarily the iris) often have the best prognosis because they are caught the earliest. Other ocular melanomas may be found after they begin to cause symptoms or when the pupil is dilated during an eye exam.

The eye is composed of several layers and tissues, including the iris, ciliary body and choroid. The iris, which is the colored area of your eye, controls how much light enters the pupil. The ciliary body changes the shape of your lens when you focus on an object and makes the transparent liquid found between the outer layer of the eye and the iris. The choroid provides blood to the front part of the eye and to the retina, which is the light-sensitive ocular tissue.

Rarely, melanoma may also develop in the conjunctiva, the mucous membrane lining the eye, which keeps the eye lubricated.

Mucosal melanoma develops in the mucosal lining of the body, a membrane that covers many body cavities and passageways. It is a rare disease accounting for around one percent of all melanomas. Because it often begins in concealed areas and causes no specific symptoms, many cases are diagnosed only after they have progressed to an advanced stage. The body’s moist mucosal linings are:

• The respiratory tract, in areas such as the sinuses, nasal passages and mouth. Head and neck mucosal melanoma is the most common type.
• The gastrointestinal tract, including the anus and rectum (anorectal).
• The female genital tract, including the vagina and vulva.

HOW MELANOMA GROWS AND SPREADS

Melanoma cells may enter the lymphatic system, a network of vessels that carry lymph (a colorless fluid) throughout the body. Once in this system, melanoma cells can spread to nearby lymph nodes and also may enter the bloodstream and travel to other parts of the body. Early treatment can stop melanoma before it spreads through the lymphatic system to lymph nodes in the region or to distant organs, which is why early detection and treatment are so important.

In the first growth stage, known as the radial growth phase, the melanoma grows horizontally, staying within the upper layer of the skin (epidermis). During this phase, melanomas are not likely to metastasize (spread to other areas).

In the next phase, the vertical growth phase, the melanoma begins to grow down into deeper layers, such as the dermis and hypodermis, as well as up into the epidermis, and the risk for metastasis increases. This occurs because the lymphatic vessels are located in the lower dermis and hypodermis, and melanoma cells can use these vessels to spread to lymph nodes. Because of this, the thickness is the most important factor in determining the prognosis of melanoma. Melanomas are classified as thin (less than 1 millimeter, or about the thickness of a credit card), intermediate (1 to 4 mm) or thick (more than 4 mm).

QUESTIONS FOR YOUR DOCTOR

• Is my melanoma thin, intermediate or thick, and how does that affect my prognosis?
• How will my melanoma be treated?
• I have a lot of moles and skin spots. Can they develop into melanoma?