Skin Cancer
(Basal Cell Cancer · Squamous Cell Cancer · Superficial Basal Cell Carcinoma · Non-Melanoma Skin Cancer)
In this condition factsheet:
The Facts on Skin Cancer
Skin cancer is a common type of cancer in Canada. It is estimated that more than 80,000 Canadians develop skin cancer each year, and that number continues to rise.
There are 3 main types of skin cancer: basal cell carcinoma, squamous cell carcinoma, and melanoma. This article deals with the first two types, which together are known as "non-melanoma skin cancer." Unlike melanoma, non-melanoma skin cancer has a low mortality rate and is often highly treatable. For information on melanoma, please see our Melanoma article.
Basal cell carcinoma (BCC) is the most common skin cancer and is also the most common cancer. It grows from the basal (bottom) layer of the epidermis (the outer layer of the skin). It almost always appears on sun-exposed skin, such as the forehead, hands, lips, or tops of the earlobes. BCC makes up about 80% of all non-melanoma skin cancers. There are 3 main types of BCC:
- Superficial basal cell carcinoma (sBCC) often appears on the chest and upper body (torso) and possibly on the face. Commonly, it is a well-defined, scaly patch that looks similar to eczema. There is also often a thin, raised border that is pearl-coloured around the affected patch of skin.
- Nodular BCC appears on areas exposed to the sun, including the head and neck. It appears as an elevated bump of skin that is usually pearl-coloured or pink.
- Morpheaform BCC appears as an ivory scar in areas that have never been injured or operated on. The tumour appears slightly raised and waxy, and is often white or yellowish in colour. The borders of the tumour are not distinct.
There are also two more unusual types of BCC: pigmented BCC (similar to nodular BCC, but with black and brown pigmented areas) and cystic BCC (bluish-grey with a fluid-filled center).
Squamous cell carcinoma is less common than basal cell carcinoma, but it is the second-most-common skin cancer. It grows from the top layers of skin, and is also found most often in sun-exposed areas.
Other types of non-melanoma skin cancer, such as Merkel cell carcinoma, Kaposi's sarcoma, or cutaneous T-cell lymphoma, are known as rare skin tumours and make up about 1% of non-melanoma skin cancers.
Causes of Skin Cancer
Like melanoma, basal and squamous cell cancers are linked to sun. Most people get the majority of their lifetime sun exposure during childhood, and it's been shown that even one childhood sunburn increases the risk of developing skin cancer later in life. But a sunburn is not needed to damage the skin. A tan is also clear evidence of ultraviolet (UV) skin damage.
People with fair skin, blonde or red hair, freckles, blue or green eyes, or difficulty tanning are at higher risk of skin cancer because they have less skin pigmentation and thus less protection from the sun. Most skin cancers typically appear after age 50.
Tumours generally grow when a normal cell suffers a mutation in its DNA, causing it to multiply without the usual restrictions. It's now believed that in basal cell carcinoma, a gene called PTC is damaged by UV radiation. This gene normally causes the cell to produce a protein that prevents runaway growth. A similar scenario may occur in squamous cell carcinoma.
Other causes of skin cancer include X-rays, skin contact with arsenic or radium, and possibly simple bad luck, in that an error can occur spontaneously in a dividing cell despite low sun exposure. A sexually transmitted cancer-causing virus called the human papillomavirus (HPV) can cause a rare subtype of squamous cell carcinoma.
Symptoms and Complications of Skin Cancer
Basal cell carcinoma (BCC) usually occurs in a sun-exposed area of the skin. It usually appears as a round pink bump, although this depends on the type of BCC (e.g., superficial, nodular, or morpheaform). Over time, it's liable to grow, and after a few months or years it may be surrounded by tiny but visible blood vessels. It often has a tendency to repeatedly crust over, heal, and then crust over again. The crusting process may involve bleeding. If left alone, it may take on a very different appearance, as the cancer eats away at the skin. The result looks as if the skin has been chewed up, with bites taken out of it. Such a tumour is called a rodent ulcer.
Superficial BCC is the least aggressive type of BCC, while morpheaform BCC is the most aggressive and dangerous form. Superficial BCC grows out from the edge and causes damage in the surrounding tissues over time. Because superficial BCC grows slowly, people do not always ask their doctors for advice right away. Early detection and treatment is often the best way to increase the chances of a good outcome in many types of cancer. Nodular BCCs grow irregularly from their edges and often remain flat. Bleeding followed by crusting or scaling over occurs commonly with this type of carcinoma. Morpheaform BCCs grow quickly and are more difficult to treat.
Squamous cell carcinoma (SCC) generally begins as a small firm lump. Most SCCs grow from actinic keratosis (AK), which is a rough, scaly skin lesion that appears on sun-exposed areas. It may be the same colour as the surrounding skin, or it may be brown, pink, or red. AK is simply a change in size, shape, and organization of skin cells. Because they can lead to skin cancer, AKs should be found and treated early.
SCCs are often red, scaly, crusted, or ulcerated. They may be itchy and slow to heal. As the squamous cell tumour grows, the skin tends to degenerate and scar tissue appears. The tumour will bleed easily if scratched, though it's not usually painful. SCC is more likely to metastasize (spread to other parts of the body) than BCC. Luckily, early treatment can lead to a good chance of survival and cure.
Complications arise when the tumour reaches tissue needed for other purposes, such as the mouth, the anus, or the eye. Generally, cancers on mucous tissue (such as the lips) are more likely to metastasize. Cancer in the webs of the fingers or thumb, or before the first knuckle of a finger, is also more likely to metastasize. Metastasis is never very likely with these types of cancer, however.
While few people die of basal cell carcinoma and squamous cell carcinoma, untreated cancers can grow and produce disfigurement. Treatment will sometimes cause disfigurement if a large amount of skin has to be removed
