Babies arrive in the world with soft, smooth, and usually flawless skin. Old men and women leave the world wrinkled, mottled, spotted, and scarred. In between, the skin replaces itself many hundreds of times and in the process accumulates enough DNA damage to make skin cancer the most common of all cancers, with more than 2 million cases occurring in the United States each year. Fortunately, most skin cancers stay put in the locations where they start. They don’t invade nearby tissues and don’t spread through the base of the skin to travel to other parts of the body. Skin cancer is largely curable by removal alone.
Different skin cells and different skin cancer names
The three most common types of skin cancer arise from cells that grow in the epidermis, or outermost layer of the skin. The inner layer of the epidermis is made up of basal cells. Basal cells regularly reproduce themselves in order to make squamous cells, which are replacement skin cells and form a middle epidermal layer. This layer also contains cells called melanocytes. Melanocytes produce melanin, the pigment that gives skin its color. The outer layer of the epidermis consists of dead skin cells that are constantly being shed. The most common skin cancers come from these three types of skin cells: basal cells, squamous cells, and melanocytes. All three types of cancer are more common in fair-skinned, light-haired, light-eyed people. All three are also related to lifetime sun exposure.
Basal cell skin cancer
Basal cell cancer is the most common type of skin cancer, accounting for 80 to 90 percent of reported skin cancer cases. It is also the most benign skin cancer. Basal cell cancers begin with errors in a cell’s DNA, which serves as instructions for building squamous cells from basal cells. The abnormal cells that are created by this damaged DNA form a tiny area of skin that is different from surrounding normal skin. Typically, it looks like a little dome, with a waxy, pale appearance. Over time it may develop tiny blood vessels around it. It might bleed easily or develop a sunken center or a crusted top. Sometimes the color may be a little darker or rosier than that of the surrounding skin.
Basal cell cancers grow slowly and very rarely travel to other parts of the body. That said, they can invade nearby tissues, and the earlier they are removed, the less likely they are to recur (and the smaller the scar caused by their removal will be). Basal cell cancers occur most commonly on areas of the body exposed to the sun, especially the scalp, forehead, and corner of the nose. They are also more common in people who have been intermittently exposed to the sun without protection. Basal cell cancers take many years to develop, and by age sixty-five, about 50 percent of the population will have developed at least one such cancer. Within five years of treatment of one basal cell cancer, one-half of patients will develop a second one. Because of the popularity of tanning, both indoors and out, basal cell cancers are now appearing in some people before middle age.
Squamous cell skin cancer
Squamous cell cancers can occur in areas of the body that are not generally exposed to the sun, like the mouth and the genital region. However, when squamous cell cancers appear on the skin, they typically develop in areas that show other signs of sun damage—wrinkling, freckling, mottling, thinning, and sagging. They may also evolve from solar, or actinic, keratoses, which are considered precancerous markers of sun damage. Usually appearing as small red spots (under a quarter of an inch in diameter), solar keratoses have some white scaling on their surfaces. Some are sore and tender, and thickening with increased tenderness can indicate a progression to a skin cancer. Squamous cell cancers can be flat and scaly patches of skin or firm, red nodules or non-healing sores. Unlike basal cell cancers, squamous cell cancers, particularly those on the lip, can penetrate deeper layers of skin and travel to other parts of the body by way of the lymphatic system, though this spread is uncommon. If many precancerous lesions are present, treatment with chemotherapeutic creams helps prevent cancer development.
Like basal cell and squamous cell cancers, melanocyte cancers, which are known as melanomas and appear similar to moles, more commonly occur in fair-skinned people and are also related to sun exposure. It is no coincidence that the highest rates of melanoma in the world are in Australia and South Africa, two highly sunny areas colonized by fair-skinned people who are genetically better suited to the gray skies of northern climates.
Melanomas must be distinguished from normal moles, which develop in virtually all people. The average adult has twenty-five moles with varying degrees of pigmentation. Many “rules” exist for helping physicians decide whether a mole might be cancerous. For example, moles that are asymmetrical in shape and color, have irregular margins, and are larger than a pencil eraser are often considered suspect. However, none of these “rules” is a reliable way to tell if a mole is cancerous. More reliable suspicions are generally based on observations concerning mole development. The development of a new mole, particularly on the back or the legs, that grows over a number of years is definitely something that should be discussed with a physician.
A full 70 percent of melanomas are what are termed superficial spreading melanomas and are curable if caught when they are less than 1mm thick. Another 7 to 10 percent of melanomas, those that are deep blue-black or purple nodules, tend to spread more readily to other parts of the body. Rarer yet are melanomas in odd locations like the eye, under a nail, on the palm of the hand, or on the sole of the foot. These, too, are more dangerous.
Like basal cell and squamous cell cancers, the treatment for a melanoma is removal. There are a variety of different ways to remove skin cancers, ranging from scraping and cauterizing to a surgical excision with microscopic monitoring to find the edges of the tumor. Cure rates are high—in the 98 percent range, particularly when the tumors are small. If a tumor does spread to nearby tissues, it can still be cured, though with more surgical scarring. Metastatic melanomas do not respond well to conventional cancer treatments as a rule but may react differently to newly developing targeted immunological treatments.
Screening for skin cancer: no controversy
In contrast to the confusion surrounding screening tests for some other types of cancer, clarity is the mark of medical advice about skin cancer. It helps if you know what to look for and to seek a medical opinion about any suspicious skin spots. Most often, doctors will recommend biopsy of a suspicious lesion as the surest way to make a diagnosis, and patients can expect that removal will be part of the cure for any cancers that are found. You won’t ever regain the skin of a newborn, but you do not need to have skin cancer.
Your role in skin cancer prevention
• Beginning early in life, protect your skin, particularly the skin on your face, scalp, ears, lips, back , arms, and hands. Use hats, shirts, and sunscreen (at least 30 SPF) to help block the harmful rays of the sun.
• Avoid prolonged sun exposure when the sun is high in the sky.
• At least once in middle age, have a professional examination of all your skin. If you are fair-skinned, and/or have sun damaged skin, heed your physician’s advice if he suggests more regular checkups. The American Academy of Dermatology sponsors free screening exams every May.
• Keep an eye on your skin and have new, enlarging, color-changing, non-healing or bleeding spots checked by a professional.