Skin cancer is the most common form of cancer in Australia, and Australia has the highest rate of skin cancer in the world. There are many different types of skin cancer. By far, the most common of these are basal cell carcinoma (BBC) and squamous cell carcinoma (SCC), which are non-melanotic skin cancers.
BCC’s are generally slow-growing tumours that almost never spread to other areas of the body. They will grow indefinitely, destroying surrounding skin and structures, and will not resolve without treatment. SCC behaves similarly to BCC but tends to grow more quickly, and in some cases, spread to other areas of the body. Melanoma is less common, however, contributes to approximately 70% of deaths due to skin cancer. These tend to spread to other areas of the body earlier than BCC or SCC, and usually before obvious tissue destruction is seen.
Skin cancer risk generally increases with age as a result of cell ageing and cell mutations. Tumours arise because of irreversible genetic changes within a single cell leading to uncontrolled growth and reduced cell death. In addition to cell ageing, there are other factors that contribute to or accelerate these cellular changes.
The primary environmental hazard is sun exposure or ultraviolet (UV) radiation. UV radiation causes direct cell damage and suppresses the skin’s immune system. It contributes to all forms of skin cancer, and while considerable damage is done in childhood, ongoing exposure through life is hazardous, especially in those with outdoor occupations. Intermittent sunburn is most important in the development of BCC, compared to SCC, where cumulative sun exposure is the greatest risk factor. Other environmental factors include exposure to arsenic, tar, radiation, burns, and chronic inflammation/wounds. These exposures are more likely to be associated with SCC.
Genetics also plays a role, and some populations are at a greater risk of skin cancers than others. This includes those with fair skin which burns easily and tans poorly, albinism, a large number of moles, a strong family history of skin cancer, and certain inherited syndromes. However those with the ability to tan are not immune to the development of skin cancer. Suppression of the immune system also increases the risk of skin cancer, and results in a greater number of skin cancers and more aggressive tumours. This is seen most often in organ transplant patients on long-term immunosuppression medication.
The majority of skin cancer can be prevented by careful sun protection, including sunscreens, from an early age, and early detection by regular self-monitoring. In those with an increased number of risk factors or a history of skin cancer, regular self-examination is important for early detection of skin cancer. Whole body photography may be of benefit to those with many or atypical moles.
People who have had a skin cancer are at increased risk of further skin cancers in the future. This risk is particularly marked in younger people and in people that have any form of immune deficiency or immune suppression. Precursor lesions, actinic or solar keratoses, develop in sun-damaged skin. They show early and superficial cell damage. These can evolve into a superficial SCC, and then invasive SCC as it invades through the skin layers.