Introduction

It may surprise people to learn that skin cancer is the commonest form of cancer in the USA, and it's becoming still more common. While prevention is extremely important -- and the subject of a separate article -- early recognition and treatment of skin cancer can help save lives. The most frequent types are melanoma, basal cell carcinoma (BCC), and squamous cell carcinoma (SCC).

Melanoma

Melanoma is not as common as the other two major types of skin cancer, but it is more deadly, and it's seen in much younger people. Melanomas account for 2% to 3% of all cancers in the USA, and its frequency is doubling every ten years. It's the commonest malignant tumor in white adults between 25 and 29 years. About 15% of melanoma patients die from the disease, 20% of them while still under 40 years of age.

The likelihood of a fatal outcome depends a lot on how deeply the tumor has penetrated when it's diagnosed. This shows why it's vital to recognize a melanoma as soon as possible. As with BCC and SCC, the ultraviolet rays of sunlight are well established as the chief culprit in causing this skin tumor. Intense bouts of exposure, such as occur in children with severe sunburns, are particularly dangerous.

Some people are also at greater risk -- those with a lesser degree of pigmentation: fair skin, blue eyes, red hair, freckles, and a tendency to burn rather than tan, are well-recognized risk factors.

Pigmented moles (naevi), which most of us have in varying numbers, are a predictor of the risk of melanoma -- the greater the number, the higher the risk. One third of melanomas arise in pre-existing moles. A family history of melanoma is also a risk factor, so that its occurrence in a first-degree blood relative (mother, father, brother, or sister) increases the risk 8-fold.

There are 4 types of malignant melanoma. Most frequent (70%) are the superficial spreading type; these can occur anywhere on the body, but more often on the upper back and legs. Next most common are nodular melanomas -- they have a dome or even sometimes a stalk, but they invade the underlying tissues quickly. Rarely, there are slow-growing tumors with clear lines on the surface, and others that are found most frequently on the hands, feet and nails.

Determining the history and the appearance of the lesion over time allows one to make the diagnosis. That's is why it's important to note carefully, at intervals, any moles that seem to be changing in any way.

The 'ABCD' approach is well recognized:

• Asymmetry -- the lesion isn't round in shape, but uneven
• Border -- the edge of the lesion is irregular, not smooth
• Color -- the surface is colored variously, from very pale to dark brown-black
• Diameter -- if this is more than 6 mm (1/4 inch) it's a warning sign

Bleeding, burning, or itching raises suspicion further. The thickness of the tumor is the single most important feature in predicting the patient's survival.

Not all unusual looking moles are melanomas, and the decision to cut one out using minor surgery is not always easy. Sometimes the physician will photograph the lesion, and have the patient come back in a short time to see how quickly things may have changed. If there is doubt, and the physician wants to take a piece of the tumor for microscopic examination (biopsy), the full thickness of the lesion as well as some normal tissue on each side must be removed, just in case there has been some microscopic spread.

Basal Cell Carcinoma

This is the most common skin cancer, sometimes called a rodent ulcer. Typically it's an irregular ulcer with a raised, rolled, pearly white edge. Lesions are seen mostly on the head and neck. If they are pigmented, a BCC may be confused with a melanoma, while a very superficial BCC can resemble a patch of dermatitis. A biopsy is essential for making the right diagnosis. BCC's grow slowly, and rarely metastasize (spread to other organs of the body). Simple surgical removal along with a 2 to 5 mm (1/8 to ¼ inch) margin of healthy skin results in a cure in over 95% of cases.

Squamous Cell Carcinoma

This is the most common skin tumor in the elderly, usually because they've experienced a lifetime exposure to solar radiation. SCCs often occur at the site of previous actinic keratosis (this sunlight-induced condition will be discussed in another article when we handle the prevention of skin tumors). The development of pain, redness, ulceration, and hardening in an actionokeratosis lesion should give rise to suspicion. As with BCCs, most SCCs occur on the head or neck; other sites include the hands, forearms, upper trunk and lower legs.

An SCC may be bumpy, reddish-brown or pink, crusted or 'eaten away'. It can be hard to demonstrate a definite edge. A full-thickness biopsy is necessary to establish the diagnosis. Small SCCs (less than 2 mm, or 1/8 inch, across) can be cured by surgical removal along with 4 to 6 mm (about 1/4 inch) of normal skin at the edges.

Growth may be rapid, and 2% to 6% of SCCs metastasize to the nearest lymph nodes, the lungs or the liver. Once metastasis has occurred, about 35% of patients will survive for 5 years.

Reducing the burden

Early diagnosis and avoidance of the main cause (exposure to excessive sun) are the best way to limit the damage caused by skin cancers. The second topic is considered in a separate article -- see link below.

A picture is worth a hundred words, especially when it comes to trying to describe different skin problems. So go to the online Atlas of Dermatology -- see the link below -- to check up how these cancers look.