Skin Cancer – An overview
Australia reports the highest rates of skin cancer in the world. Melanoma and non-melanoma skin cancer are the most commonly diagnosed cancers in Australia each year.
Approximately two in three Australians will be diagnosed with skin cancer by the age of 70.
Skin cancer is primarily a preventable cancer.
What are the common types of skin cancer?
Skin cancer is divided broadly into non-melanoma skin cancer (NMSC) and melanoma skin cancer.
1. NMSC
The two most common forms of NMSC are basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). NMSC develop in the skin’s top layer known as the epidermis.
- BCC is the most common type of skin cancer, making up more than 75% of all skin cancers. BCC develops from the basal (bottom) layer of the epidermis. BCCs are slow growing. They rarely spread to other parts of the body, and are almost always completely cured by treatment. However, if left untreated, BCCs have the potential to invade and destroy the surrounding skin and tissues.
- SCC develops from squamous cells in the epidermis above the basal layer. While most SCCs are easily treated, some SCCs spread to other parts of the body including the lymph nodes and other organs.
- Bowen’s disease, otherwise known as SCC in-situ, is a superficial form of SCC. It is confined to the epidermis but has the potential, over time, to become a fully developed SCC, involving the deeper layers of the skin.
- Actinic keratoses are precancerous growths associated with sun related skin damage. They have a small risk of transforming into SCCs over time. Overall, they serve as risk markers for the future development of skin cancer.
Most NMSCs are located in sun-exposed areas of the skin. Treatment depends on a number of factors including the skin cancer subtype, the location of the skin cancer and individual patient factors. Treatments may include cryotherapy, topical agents, surgery and radiotherapy.
2. Melanoma
Melanoma occurs as a result of the malignant transformation of melanocytes, which are the pigment producing cells of the skin located at the bottom of the epidermis. Melanoma can develop anywhere on the skin but most commonly occurs on the trunk in men and legs in women. In rare cases, melanoma can develop in other relatively unexposed areas where melanocytes are also found such as acral surfaces (palms and soles), the nail bed, mucosal areas (mouth, genitals) and ocular surfaces (eyes).
More than 70% of melanomas are thought to arise as new lesions, while a smaller percentage may arise from pre-existing moles (either normal or atypical moles). In 20% of cases, melanoma may be amelanotic where the lesion has little or no pigment and may appear predominantly red in colour. The “stage” of the melanoma (primarily the depth of the melanoma), determines the likely outcome. Early detection and diagnosis of melanoma is associated with a greater chance of survival. Melanomas detected in their early stage are almost always cured by removal. If not detected early, melanoma has the capacity to spread to other parts of the body, including lymph nodes and organs.
3. Less common types of skin cancers include:
- Merkel cell carcinoma – often rapidly growing amelanotic nodule that has a very poor prognosis
- Atypical fibroxanthoma – a skin tumour commonly located on the head and neck region, typically occurring in heavily sun damaged skin.
What is the cause of skin cancer?
Skin cancer is the result of DNA damage to exposed skin cells from overexposure to UVA and UVB radiation from the sun or solariums. Over time, mutations caused by excessive UV, such as from childhood sunburn or long-term occupational exposure, can accumulate and trigger changes in skin cells that can lead to cancer.
There is direct evidence that sun exposure is the cause of mutations in critical tumour suppressor genes in BCC, SCC and melanoma, which allows initiation of tumour development.
Other risk factors for skin cancer, in addition to UV exposure from sunlight and tanning beds or solariums, include: the total number of moles that a person has; the number of atypical (dysplastic) naevi (moles); skin, hair and eye colour; having a depressed immune system; and having a personal or family history of NMSC or melanoma.
How can skin cancer be prevented?
Minimising UV exposure and using effective sun protection has been shown to prevent the development of photo aging (photodamaging and ageing effects of the sun on the skin), actinic keratosis, SCC, BCC and melanoma.
Minimising UV exposure is key to minimising skin cancer risk; with utilisation of sunscreen, broad spectrum SPF 50, appropriate hat wear (broad brimmed), sun protective clothing, use of sun protective eye wear, avoiding UV exposure during the peak periods of the day and seeking shade where possible. Useful aids to the UV index and sun protection include the Sunsmart application. Regular skin self-surveillance, particularly monitoring for new or changing lesions, accompanied by annual review by your local doctor or dermatologist, depending on your risk profile and past history, is key to early diagnosis and prevention.
There are new preventative therapies available such as oral nicotinamide (vitamin B3) for those with an established history of NMSC. A recent Australian study demonstrated a significant reduction in NMSC in those who took high dose oral nicotinamide (500mg twice a day) for a year.
Further information about skin cancer
Visit ACD’s Position Statements, Consensus Statements and Factsheets page for more information about skin cancer statistics in Australia, including information for patients and health professionals.
This information has been written by Dr Annika Smith
Last updated: October 2022