What is skin cancer?
Skin cancers are a group of cancers that originate from abnormal skin cells. They differ according to the type of skin cell that the cancer originates from. The most common types of skin cancers are melanoma, basal cell carcinoma and squamous cell carcinoma.
The cause of skin cancer, as with other cancers, is damage to cellular DNA. This damage results in uncontrolled cell growth leading to tumour formation. Tumours can invade nearby tissue, or cells can separate from the original tumour and spread throughout the body by the bloodstream or lymphatic system. Damage to skin cells usually results from exposure to ultraviolet (UV) radiation, which can come from sunlight, but also solarium tanning beds. The lifetime exposure, pattern of exposure and intensity of the UV radiation all influence the development of skin cancer.
Skin cancer can originate in melanocytes, basal and squamous skin cells.
Risk factors for skin cancer include:
- Age – the risk of skin cancer increases with age;
- UV radiation exposure – either short but intense exposure to UV which causes sunburn, or long-term, accumulative exposure such as working outdoors;
- Sun-tanning or using tanning beds;
- Having a family history of skin cancer;
- Having fair skin, and;
- Having a weakened immune system.
Basal cell carcinoma
Basal cell carcinomas originate in basal cells, which are located deep in the outer layer of skin (epidermis). Basal cell carcinomas tend to grow slowly and invade only nearby tissues. They don’t spread to other areas in the body.
Squamous cell carcinoma
Squamous cell carcinomas start in squamous cells, which form most of the epidermis. They are capable of spreading to other areas of the body.
Melanoma is a cancer of specific cells called melanocytes, which are also located deep in the epidermis. Melanocytes produce the pigments that give skin its colour. Therefore, most melanomas are dark or pigmented, however a few may be pale or normal skin colour. Melanomas can spread to other areas of the body.
Signs and symptoms
Methods for diagnosis
Medical history and physical exam
Your doctor may ask you questions about any concerning skin lesions, such as its duration, any recent changes and whether it is tender. Your skin may be thoroughly examined for other skin lesions, any swollen glands and signs of sun damage to the skin. A special hand-held magnifying device, called a dermatoscope, may be used to further characterise concerning skin lesions.
A skin biopsy is a tissue sample taken for microscopic examination in the laboratory. A local anaesthetic may be used during biopsies. There are three types of skin biopsies that may be performed, depending on the type, size and location of the skin cancer:
- Incisional biopsies, which involve the removal of the entire abnormal area of skin with a scalpel;
- Punch biopsies, which involve the removal of a small circle of the whole skin layer, much like a hole puncher removes holes in paper, and;
- Shave biopsies, which involve shaving off the top layer of skin.
Punch biopsy involves removing a small section of the skin for cancer diagnosis.
The skin biopsy will be examined under a microscope to look for changes typical of skin cancer.
The following tests may be performed to assess if the skin cancer has spread to other areas of the body, particulary for melanomas and large squamous cell carcinomas:
A chest X-ray uses X-ray beams to create an image of your chest’s internal structures. It can show masses such as metastases in the lungs, or enlarged lymph nodes.
Computerised tomography (CT) scan
A computerised tomography scan uses X-rays to develop a 3D image of the body. It has a higher sensitivity than X-rays and therefore can detect smaller tumours.
Magnetic resonance imaging (MRI)
Magnetic resonance imaging is like a CT scan, but uses a magnetic field and radiofrequency radiation instead of X-rays. Both CT and MRI scans generally show very detailed images of tumours and their sites of spread.
Positron emission tomography (PET)
Positron emission tomography, or a PET scan, requires the injection of a radioactive label, or tracer. A CT scan will then produce images that will show up any abnormal cell growth highlighted by the tracer.
Types of treatment
This treatment involves surgical removal of the abnormal tissue. Depending on the type of skin cancer, the tumour and a recommended border of surrounding normal tissue are removed. Small basal or squamous cell carcinomas can often be removed simply under a local anaesthetic. In the case of melanoma, a more complex surgery under a general anesthetic may be required, involving a wider excision of the affected area as well as removal of nearby lymph nodes.
Cryosurgery involves using a device, the tip of which is cooled with liquid nitrogen or nitrous oxide, to freeze and destroy abnormal tissue. This may be used for small basal cell carcinomas, but is generally not suitable for melanomas and large squamous cell carcinomas.
Electrodessication and curettage
Electrodessication and curettage is a simple surgical technique. It involves using an instrument called a curette, which looks like a spoon with a sharp edge, to remove the tissue. This is followed by electrodessication, which uses an electrode to apply an electric current to the tissue to stop (cauterise) any bleeding.
Mohs’ micrographic surgery
During this type of surgery, the skin is removed one thin layer at a time and immediately examined under a microscope for presence of cancer. The cancerous areas are then removed until no trace of the cancer is found in the examined layers.
Most of the following therapies are relevant to melanoma, however, some may occasionally be required for more serious cases of squamous or basal cell carcinoma. It is important to note that smaller melanomas that have been completely excised surgically and have not spread may not need any chemotherapy or radiotherapy.
Adjuvant therapy is given after the first line of treatment, with the aim of preventing the cancer from returning. It can take the form of radiotherapy, chemotherapy or a combination of these treatments.
Like adjuvant therapy, neoadjuvant therapy also uses either or both of the radiotherapy or chemotherapy treatments, but prior to surgical excision.
Chemotherapy is the use of specific drugs developed to target cancer cells and stop their reproduction. Various medications are used, which can be administered intravenously or orally.
Chemotherapy can be given as adjuvant chemotherapy, which is given after surgery with the aim of preventing the cancer’s return and/or neoadjuvant chemotherapy, which is given prior to the surgery to help shrink the tumour before its removal. It involves giving one or more medications, administered in cycles, followed by a rest period.
Side effects occur because chemotherapy can also affect healthy cells. Your doctor will monitor your dosage carefully to achieve an optimum therapeutic effect.
In this type of therapy, focused X-rays from an external beam radiation source are applied to the area where the tumour is located. Radiotherapy can be used alone, or in addition to surgery and/or chemotherapy.
Immunotherapy is the use of medication that acts on the immune system. Interferons, immunisation with dendritic cell vaccines, extracts of patient melanoma and synthetic melanoma antigens are some of the various immunotherapies used for melanoma.
Some melanomas have a specific gene mutation in the BRAF gene, causing production of a particular protein involved in cell signalling and growth. The production of this protein can be targeted, or blocked, by certain medications, thereby slowing the growth of cancerous cells.
Some people diagnosed with cancer seek out complementary and alternative therapies. None of these therapies are proven to cure cancer, but some can help people feel better when used together with conventional medical treatment. It is important to discuss any additional treatments with your doctor before starting them.
Skin cancers have the potential to spread locally or to other areas of the body. Basal cell carcinomas typically invade surrounding tissues, if left untreated. However, they do not spread to other areas of the body. However, squamous cell carcinomas and melanomas have the potential to spread to other areas of the body. They can spread via the bloodstream and lymphatic system. In the case of squamous cell carcinomas, they have a tendency to also spread through local nerves. Local or wider spread of skin cancers complicates treatment, may reduce success of cure, and can cause disability and potentially death.
The best way to prevent skin cancer is by minimising your exposure to UV radiation, which can be done by avoiding sunlight during the times specific to your state,1 wearing protective clothing such as hats and long-sleeved shirts with collars and frequently applying sunscreen. Avoiding sun-tanning and tanning beds is one of the easiest things you can do to help lower your risk.
Minimising exposure to UV radiation by wearing a hat, protective clothing and sunscreen may prevent skin cancer.
Last Reviewed: 03/10/2018
Your Doctor. Dr Michael Jones, Medical Editor.