Squamous cells are skin cells that make up most of the outer layer; basal cells are found at the bottom of the skin’s outer layer (the epidermis). Cancer of either of these types of skin cells is known as a carcinoma. While melanoma is a cancer of the melanocytes, basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) are cancers of the keratinocyte—the skin cells that distribute the melanin released by melanocytes. While usually not fatal, BCC and SCC can spread to other parts of the body and cause serious health consequences.
Both BCC and SCC occur almost exclusively in skin that was exposed to the sun, usually in people with fair skin.8 They usually do not appear until adulthood, as they are the result of accumulative damage from UV radiation. If discovered and treated early, 95% of all BCC and SCC cases are cured.7
Basal cell carcinoma (BCC) is the most common type of skin cancer in the United States,9 diagnosed in 800,000 people each year. It has traditionally been seen most commonly in the elderly, but the age of onset is steadily decreasing. BCC tumors usually appear as small, fleshy bumps, often on the head or neck. They can, however, appear in other areas of the body as well (usually sun-exposed areas).7 BCC can often resemble other skin conditions such as psoriasis and eczema, so it is important to have any skin problem examined by a dermatologist. BCC tumors grow slowly and rarely metastasize; however, if unchecked, they can grow downward into the bone and cause serious damage.7
SCC is the second most common skin cancer in the United States, affecting more than 200,000 people every year. Like BCC, it is usually caused by chronic exposure to sunlight and other sun damage is usually present in an area that develops SCC. However, SCC can also occur in areas of the skin that have been damaged by burns, scars or chemicals. People with medical conditions that produce chronic skin inflammation or suppress the immune system are at increased risk for SCC. Occasionally it also occurs in skin that has not been exposed to the sun; the tendency to develop this condition may be hereditary.
SCC tumors appear as nodules or red, scaly patches of skin, most often on the rim of the ear and the lower lip.7 They can also appear as a wart-like growth that crusts and bleeds occasionally or open sore that won’t heal. Tumors can grow into masses that cover large areas of the body. Unlike BCC, SCC is capable of metastasizing to other areas of the body.7 Metastasis occurs only in a small percentage of cases, but if SCC spreads to other tissues and organs, it can be fatal.
Melanoma is the most common fatal skin cancer and it is also one of the most common skin cancers in young adults.2 Melanoma often occurs at a younger age than BCC or SCC because it is caused by intermittent intense exposures to UV radiation, as opposed to cumulative damage over a lifetime.
Melanoma occurs when melanocytes damaged by UV radiation begin to divide out of control. Keratinocytes (which are responsible for BCC and SCC) undergo the most damage when they are repeatedly exposed to low doses of UV radiation—for example, in people who develop a tan. Melanocytes, on the other hand, are most harmed by occasional exposures, such as the kind that cause a sunburn. These differences explain why BCC and SCC are usually found on chronically sun-exposed areas (such as the face, the forearms and the backs of the hands) while melanoma usually occurs on areas not often exposed to the sun (such as the back in men and the lower legs in women). Melanoma rarely occurs on the face, hands or forearms.2
The risk of melanoma is doubled in people who have had five or more severe sunburns (especially burns that blistered) during adolescence.2 Fair-skinned people (especially those with freckles) are at the highest risk for melanoma and the risk for whites is also affected by latitude (the closer to the equator, the greater the risk). Blacks and Asians tend to develop melanoma in areas of the body not exposed to the sun—such as the nail beds and the soles of the feet.2
Another strong risk factor for melanoma is the presence of dyplastic nevi (abnormal or unusual moles). Not all dysplastic nevi will become malignant and researchers have not been able to figure out why having these moles increases the risk of melanoma. Melanoma does tend to run in families, so if two or more family members develop the disease, first-degree relatives (parents, siblings and children over the age of 10) should be screened for dyplastic nevi or other evidence of melanoma.
Melanoma lesions usually resemble a mole, but one that is asymmetrical, has irregular shape or borders, has varying colors and is larger than 6 mm (about the size of a pencil eraser).4 However, while most melanomas fit this description, not all do. It is important to examine your skin regularly for anything unusual. If you notice that a mole is changing (especially developing black areas), or if you see a new or “ugly-looking” mole, see your primary care doctor or dermatologist as soon as possible.
Most likely as a result of increased awareness, an increasing percentage of melanomas have been diagnosed at an early stage in the past few decades. Most people (more than 85%) diagnosed with melanoma are cured.4 Early-stage tumors are often thin (meaning they don’t extend deep into the surface of the skin) and can be removed by minimally invasive surgery.
Few effective therapies exist for late-stage melanoma, however, and the disease is likely to spread to almost any organ in the body.4 Surgery is required to remove the original growth and nearby lymph nodes may have to be removed as well. Advanced melanoma is usually treated with immune therapies (such as interferons and interleukin-2), but these measures are not very effective.4
The five-year survival rate for all people diagnosed with melanoma is 89%. However, the rate is 96% for those with localized melanoma; 60% for people with regional metastases; and 14% for those with distant metastases.
How to protect your skin
Since aging skin is especially vulnerable to the effects of UV radiation, it is important to prevent new damage from occurring. The easiest way to avoid UV radiation is to avoid sun exposure, especially between the midday hours, when UVB radiation is at its peak. However, UVA levels are high from sunrise to sunset and even avoiding direct sunlight does not protect us from all UV radiation. Half of our exposure to UVA radiation occurs when we are in the shade, so it’s important to employ sun protection whenever you’re going outside. (Also, remember that sunlight is an important component in the body’s production of vitamin D, so older adults who are avoiding sun exposure should drink vitamin-D fortified milk or take a vitamin D supplement to ensure good calcium absorption and help prevent osteoporosis.)
Two other simple steps can help prevent sun damage to your skin. Wear a long-sleeved shirt and long pants whenever possible and always wear a wide-brimmed hat to protect your head and neck from the sun.
Of course, sunscreen is an important step in protecting against UV damage. A recent study of more than 1,600 adults ages 25 to 74 in Australia found that daily sunscreen use helped minimize the development of actinic keratoses, which are associated with squamous cell carcinoma. After two years, the group that used sunscreen daily had 24% fewer actinic keratosis lesions (one fewer lesion per person) than the group that followed their normal sunscreen regimen.6
There is other evidence that using sunscreen, even after previous UV damage, can help improve skin quality. However, it appears that many people are not using sunscreen correctly and may not realize it. Researchers at the University of Texas surveyed sunscreen use during one summer day at the beach. More than three quarters of the people who said they applied sunscreen that day left the beach with a sunburn. The eight people who did not burn said they reapplied sunscreen every one to two hours and also after swimming.10
In addition to not applying sunscreen often enough, it appears that people just aren’t using enough sunscreen during each application. The average adult needs an ounce of sunscreen (the amount that would fill a shot glass) to cover his or her body adequately.10 It’s also important to apply sunscreen prior to or immediately upon sun exposure—a sunburn can occur in as little as 10 minutes in some extremely sunny areas.
Even if you apply sunscreen religiously, however, it’s a good idea to limit your time in the sun. You may not be getting a sunburn, but UV radiation may still be causing DNA damage and suppression of the immune system.11