Overview

What is Skin Cancer?

Skin is made up epidermis, dermis and subcutaneous tissue. Epidermis is a kind of squamous epithelium. In the epidermis, the actively dividing basal cells mature to become keratinocyes. Subsequently, the keratinocyes lose their nuclei and die and become keratin. Interspersed between the basal cells are pigment-producing cells called melanocyes. Skin cancers are malignant tumours of the basal cells, keratinocyes and melanocytes.

How common is Skin Cancer?

According to the Trends in Cancer Incidence in Singapore 2004-2008 (Singapore Cancer Registry), there are 1065 cases of skin cancer and 941 in Singapore men and women yearly respectively. Skin cancer ranks 8th in both men and women in Singapore.

Types of Skin cancer

Skin cancers are divided into melanoma and non-melanoma skin cancer (NMSC). In Singapore, NMSC are much more common than melanoma. Melanoma behaves much more aggressively than NMSC. Melanoma is the malignant tumour of the melanocytes. NMSC consists of squamous cell carcinoma (SCC) and basal cell carcinoma (BCC). In normal population, BCC is more common than SCC. Solid organ transplant recipients have higher rate of skin cancer. SCC is more common than BCC in solid organ transplant recipients.

Causes and Risks

BCC is the most common skin cancer and is most common in the sun-exposed area. The most common complaint is bleeding or scabbing sore that heals and recurs. BCC is slow growing and may grow for many years before presentation to the doctor. There are several types of BCC. In Singapore, the pigmented BCC is relatively common and may be mistaken for a mole. Although BCC can be locally destructive, it rarely spread (metastasis).

SCC is the second most common skin cancer in Singapore. There are 3 types of presentation of SCC. SCC may arise from actinic keratoses that look like thick adherent scales. These SCC are soft and freely movable and are located on the bald scalp, forehead, ears and backs of the hands. The second type of SCC appears in sun-damaged skin. They are firm, movable, elevated mass with sharply defined border and little surface scale. These SCC have minimal potential to metastasis but may be locally aggressive. The third type of SCC arises from normal skin or the lip. They are aggressive and metastasize to regional lymph nodes.

Melanoma is the most dangerous skin cancer because the ability to metastasis early. It is the least common skin cancer in Singapore. There are several types of melanoma. The acral lentigenous melanoma is the most common type of melanoma in Singapore. They appear on the palms, soles or the under the nails of toes and fingers. The melanoma may arise from normal appearing skin or an existing pigmented growth. The ABCDE rule of melanoma stands for Asymmetry, Border, Colour (haphazard combination of many colours), Diameter over 6 mm and Evolving (enlarging) of a pigmented growth. Therefore, it is important to consult a doctor if there is any change of a growth on the skin.

Diagnosis

Diagnostic Tests

Skin biopsy is used to diagnose skin cancer. It is a simple procedure done under local aneasthesia. Either part of the suspected growth or the whole growth if it is small is removed and sent to the pathologist. The pathologist will examine the specimen under the microscope and confirm the diagnosis. The pathologist will also determine the histologic type (cell type of the cancer cells), the thickness of the cancer (depth of invasion) and other characteristics of the skin cancer.

Other tests such as lymph node biopsy, blood test and imaging may be required for staging, treatment and prognosis.

Treatment Options

Treatment of Skin Cancer

The main stay of treatment is excision with adequate wide margin. If the skin defect is large after excision, skin graft may be required. Moh’s microsurgery is a microscopically guided way to remove skin cancer. Other forms of treatment include cryotherapy (freezing with liquid nitrogen) and curettage and electrosurgery, photodynamic therapy and radiation therapy. FDA has approved imiquimod cream to treat superficial BCC and SCC. Metastasis of melanoma can be treated with interferon alpha-2b, interleukin 2 and chemotherapy.

Prognosis of Skin Cancer

The prognosis depends on the histologic type of the malignant cell, tumour size, depth of the tumour, location of the tumour and the presence of metastases. Excision with adequate wide margin can promise a cure for most of the early skin cancers. There are guidelines to the excision margin of the various skin cancers. The early detection of skin cancer cannot be overemphasized. The prognosis for thick melanoma with wide spread metastasis is grave. All patients should be followed up to detect local recurrence, metastases and additional skin cancers.

Prevention

Ultraviolent radiation from the sun is the most important risk factor of melanoma and NMSC. Sun avoidance and the use of sun protection devices such as hats, umbrella, clothing and sunscreen should be started from young. Self-examination and awareness can help early detection of skin cancer.