By Dr Derrick Aw, Consultant, University Dermatology Clinic, National University Hospital.

When we think of skin cancer, we often think that only Caucasians with fair skin are prone to it. However, skin cancer is actually the seventh most common cancer in males (eighth for females) in Singapore.

The most common skin cancers are basal cell carcinoma, squamous cell carcinoma and melanoma. All three are related to cumulative effects of sun exposure, and hence are most frequently found on sun-exposed areas of the body in older people, particularly those between age 50 to 70.

How does skin cancer develop?

Cancer arises from an unchecked growth of cells that have become abnormal for some reason.

When cancer occurs on the skin, it may be the direct result of the abnormal skin cells, or due to ?spread? from another primary source of cancer (such as skin elsewhere or an internal organ).

Basal cell carcinoma

This is the most common skin cancer.

It typically manifests as a slow-growing, semi-transparent bump on the face which may bleed, crust or ulcerate. In our local setting, this bump may appear dark-coloured. If you look carefully, you can often find small superficial blood vessels or "telangiectasias" on its surface.

If left alone, it continues to enlarge slowly over months to years. It may invade deeply, causing local destruction and disfigurement. It very rarely spreads elsewhere.

Squamous cell carcinoma (SCC)

This is the second most common skin cancer.

It typically appears on a sun-exposed area as a fairly rapidly-growing bump that is hard, dry and rough. It may grow outwards to resemble a cauliflower, or ulcerate.

SCC most often develops from a pre-existing actinic keratosis. This appears as a small scaly or crusty bump which feels dry, rough and horn-like. It is most often found on the forehead, the balding parts of the scalp and the rims of the ears.

Actinic keratosis is not life-threatening, but the lifetime risk of progression of transformation to SCC has been estimated to be up to 10%, hence it is important to treat it.

SCC may also develop from chronic wart viral infections or sites of chronic skin damage, such as a burn scar or a longstanding ulcer.

• Other risk factors for development of SCC include
• Chronic arsenic poisoning (i.e. arsenic was found in certain herbal medicines used to treat asthma in the past)
• Industrial exposure to hydrocarbons (i.e. tar)
• Previous radiation therapy
• Smoking
• Organ-transplant recipients on lifelong treatment which suppresses their immunity.

If left untreated, SCC may spread to the lymph nodes and other parts of the skin or internal organs.

Melanoma

This form of skin cancer arises from cancerous transformation of pigment cells, either from normal skin (about 50% of melanomas) or a pre-existing mole or freckle.

Risk factors for melanoma are:

•  Fair skin complexion
•  History of excessive sun exposure
•  Family history of melanoma
•  Presence of large numbers of moles
•  Presence of large ( > 20cm in adult) mole which appeared at birth
•  Presence of atypical moles. Atypical moles may run in the family, appear larger than common moles (5-15mm in diameter), have more irregular borders and varied colours, and are found on sun-covered areas too.

The first sign of a melanoma is usually a changed or new mole or freckle. Its shape and colour may appear irregular or unusual.

In Asians, melanoma is most often found in the palms and soles. This is known as acral lentiginous melanoma.

Melanoma may also arise on the nailbed, and it manifests as diffuse nail discoloration or a longitudinal pigmented band within the nail plate. Like SCC, melanomas are sinister cancers that can spread quickly to the lymph nodes and internal organs.

How is skin cancer treated?

The treatment of a skin cancer depends on the type of cancer, its extent (local and distant) and the patient's state of health.

There are numerous treatment methods, such as:

• Surgical removal
• Electrodessication (using an electric current to kill the cancer cells)
• Curettage (scraping with a spoon-like instrument)
• Cryosurgery (freezing using liquid nitrogen)
• Radiation therapy
• Chemotherapy (either cream or injection).

The best strategies against skin cancer

Early detection and prevention of skin cancer remain the best strategies.

Skin cancer should be suspected if one has a new growth or a sore that does not heal. Look out for moles that change - the warning signs are:

• Asymmetry
• Border irregularity
• Colour variation (turning lighter or darker or mottled)
• Diameter ( > 6mm in size)
• Evolving (becoming itchy, painful, bleeding, ulcerating, or enlarging out of proportion to the other moles on the body) and
• Family history of skin cancer

National University Hospital has a dedicated skin clinic that offers skin cancer screening and surveillance for people with many ( > 10) moles, moles on inconspicuous sites (such as back, buttocks), people with a personal or family history of skin cancer, people with large ( > 20cm in adult) mole from birth and organ-transplant recipients on immuno-suppressive treatments.

People who have had received extensive sun exposure in the past are also welcomed to undergo skin cancer screening.

Stay out of the sun

Sun avoidance is a universal advice if you want to reduce your risk of skin cancer.

Using a sunblock of SPF 15 and above helps to minimise sun exposure. Sunblock should be applied on 30 minutes before going into the sun. You should use it liberally and rub it in well. Apply the sunblock everywhere the sunrays may touch you, even over the ears and back of the neck.

Not all sunblocks are the same. Make sure you choose the appropriate one for the type of activity you are going to engage in.

For example, if you intend to swim, you should use a water-resistant or water-proof sunblock. If you sweat a lot, you should use a sweat-resistant or sweat-proof sunblock. If you swim or sweat for long hours, you should reapply the sunblock frequently (such as hourly). Of course, it would be wise to avoid the sun during the 'peak' hours between 10am - 4pm!

This article is contributed by National University Hospital, Singapore.