Skin cancer is the most common type of cancer in Canada. It is estimated that more than 78,000 Canadians develop non-melanoma 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 75% 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.
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
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.
Making the Diagnosis
Skin cancer is diagnosed by taking a skin sample from the suspect lump or spot, and examining it under the microscope. This is called a biopsy. Normally, there's no need for a major examination to check for cancer that has spread throughout the body, as this rarely occurs.
There are three main types of biopsy used to confirm the presence of non-melanoma skin cancers. The types of biopsy include:
Depending on the type of biopsy, either a part or all of the affected area is removed. All these biopsies require local anesthetic before the procedure.
Treatment and Prevention
Skin cancer is usually treated with surgery. People with removed cancer are never told that they're completely cured because there's always a chance that the cancer will return, because some cancer cells may have spread beyond the removed tissue. To lessen this risk of recurrence, surgeons typically cut an extra margin around skin tumours.
Higher-risk tumours like hand or lip tumours are often removed using Mohs micrographic surgery, in which a specially trained surgeon removes skin in layers using a microscope to follow the exact spread of cancer cells. People who have been treated with this technique have a lower rate of cancer recurrence.
Occasionally, tumours are killed by freezing them with liquid nitrogen or burning them with a laser. Radiation and chemotherapy can be used in addition to surgery if the cancer has recurred or if your doctor believes it might metastasize or return.
Topical medications (medications that are applied to the skin) can be used to treat superficial basal cell carcinoma (sBCC). These medications include 5-fluorouracil* (also known as fluorouracil) and imiquimod.
5-fluorouracil (5 FU) belongs to the group of medications known as topical antineoplastics. It works by interfering with cancer cell growth.
Imiquimod belongs to the group of medications called immune response modifiers. This type of medication works by stimulating the immune system to produce substances that fight against the cancer.
In cases where the cancer has spread to other areas of the body, chemotherapy medications may be used in combination with other treatment options such as radiation therapy and surgery. Your doctor will decide on an appropriate combination of medications based on your individual medical history.
To help prevent skin cancer, protect your skin from the sun by covering up with clothing or wearing a sunscreen that has an SPF of at least 30 and blocks both UVA and UVB rays. Apply a generous amount of sunscreen to your body at least ½ hour before going outside. Reapply the sunscreen on a regular basis, especially after swimming or sweating. Check your skin every month for changes, growths, or sores that do not heal, and have these checked out by a doctor as soon as possible.