The Sunburned Country: Skin Cancer in Australia
Skin cancer is a significant public health issue in Australia. Exposure to ultraviolet radiation emitted by the sun in the UVA and UVB wavelengths is the primary cause. Australia has been a world leader in efforts to protect the ozone layer, the main line of defense against ultraviolet radiation emitted by the sun. Ultraviolet radiation induces the formation of thymine dimers that cause mutation of skin cells if not repaired before DNA replication. Mutations of tumor suppressor genes can lead to uncontrolled cell growth. Ultraviolet radiation also causes immunosuppresion that allows skin cancers to become established. Basal cell carcinoma, squamous cell carcinoma, and melanoma are types of skin cancer caused by sun exposure, though each form is associated with a different pattern of exposure. Australia has the highest rate of skin cancer in the world, due to a combination of tropical latitude, fair-skinned population, outdoor lifestyle, and high amount of ambient ultraviolet radiation. Widespread opinions about tanning and health benefits of sunlight lead many Australians to intentionally overexpose themselves to the sun. State cancer councils have developed sun safety and awareness campaigns, such as “Slip! Slop! Slap!” and “SunSmart,” to educate the population about sun exposure and encourage early detection of skin cancers. Gradual changes in knowledge and behavior indicate that the fight against skin cancer can be won.
Australia has the highest rate of skin cancer in the world. The combination of the predominantly light-skinned population, tropical latitude, and cultural emphasis on out-door activities have contributed to this problem. The Australian government has taken measures to educate the public, reduce skin cancer rates, and advocate early cancer detection. Australia is also active in global efforts to reduce destruction of the ozone layer, the main protection against the ultraviolet radiation that causes skin cancer. Numerous studies have been conducted in Australia on many aspects of skin cancer including those on the molecular biology of the cancer cells, ultraviolet-induced mutagenesis, social and behavioral aspects of skin cancer risk, and the effectiveness of government programs to combat cancer.
Ultraviolet Radiation and the Ozone Layer
Ultraviolet radiation is divided into three types based on wavelength. UVA radiation is the longest wavelength, 315-400 nm, and is just slightly shorter than visible light. UVB is radiation of wavelength 280-315 nm. UVC, the highest energy radiation, has wavelength below 280nm (de Gruijl 1999). Each of these forms of ultraviolet radiation is harmful to living cells.
The primary line of defense against harmful ultraviolet radiation is the ozone layer in the stratosphere, 15 to 30 km above the surface of the earth (Australian Government Department of the Environment and Heritage 2003). Approximately 2 billion years ago, molecular oxygen produced by early life on earth began to increase the atmospheric O2 content. Molecular oxygen in the upper atmosphere absorbs short-wave UVC radiation and decomposes to form singlet oxygen, O. When these O atoms encounter molecular oxygen (O2) molecules, they react to form ozone, O3. The O3 molecules absorb UVB radiation up to about 310 nm in wavelength. The ozone layer screens out all of the UVC and much of the UVB radiation emitted by the sun, protecting life on earth from these high-energy wavelengths (de Gruijl 1999).
The ozone layer plays a critical role in the battle against skin cancer by blocking out much of the ultraviolet radiation from the sun. Any increase in the amount of UVB reaching the earth has a significant impact on human health. Studies on the mathematical relationship between the ozone layer, ultraviolet radiation, and skin cancer incidence estimate that a 1% reduction in ozone concentration will increase UVB radiation exposure by 2%. This will cause an increase in the incidence of non-melanoma skin cancers of between 3% and 6%, and an increase in the incidence of melanoma by between 1% and 1.5% (Kripke 1988).
This increase in skin cancer incidence is a delayed effect. A patterned increase in skin cancer occurrence takes several decades to develop, and measurable decreases in ozone concentration have been reported for approximately thirty years. Adults with skin cancer twenty years ago were not likely impacted by the increase in UVB exposure as children. Therefore, ozone depletion was probably not the cause of the initial increase in skin cancer incidence reported ten to twenty years ago (Kripke 1988). The impact of ozone depletion on the occurrence of skin cancer will become more apparent as those born the last thirty years reach adulthood.
Ozone Protection in Australia
The ozone layer has been depleted in recent decades by the use of substances that upset the balance of chemical reactions taking place in the stratosphere. These substances include chlorofluorocarbons, halons, methyl chloroform, carbon tetrachloride, hydrochlorofluorocarbons, and methyl bromide. They are used in a variety of ways in refrigeration, dry cleaning, solvents, and fire extinguishers. There has been a 5% to 9% depletion of the ozone layer over Australia since the 1960s (Australian Government Department of the Environment and Heritage 2003).
Australia has been a world leader in efforts to protect the ozone layer. In 1994, The Australian and New Zealand Environment and Conservation Council banned the production of halons. A ban on chlorofluorocarbons followed in 1996, as well as controls to phase out hydrochlorofluorocarbons. Numerous ozone protection acts are also in place on the state level in Australia (Environment Protection Authority 2003).
In addition to enacting state and national level legislation regulating ozone-depleting compounds, Australia was a major player in the development of the Montreal Protocol, the first international cooperative effort to protect the global environment. The original Montreal Protocol was signed in 1987 and set measures for worldwide control of the production and use of substances that damage the ozone layer. It has been revised eight times since then to reflect advances in technology. These advances allow more environmentally friendly practices to replace ozone damaging activities more quickly than originally planned. Australia makes annual contributions toward the Montreal Protocol and also spends AUS$4.2 million each year to help developing nations reduce their dependence on ozone-depleting substances (Environment Protection Authority 2003).
Types of Skin Cancer and Sun Exposure
The three most common forms of skin cancer are Squamous Cell Carcinoma (SCC), Basal Cell Carcinoma (BCC), and melanoma. Ultraviolet exposure patterns are specific to the development of each type of skin cancer, and each type has its own pathological characteristics.
SCC is related to total lifetime sun exposure and a pattern of continuous exposure (Armstrong and Kricker 2001). Damage accumulated over time results in tumors on highly exposed skin, such the face, neck, and backs of the hands. SCC is not nearly as aggressive as melanoma, but SCC tumor cells can metastasize and become life threatening if not identified and treated early (de Gruijl 1999).
BCC is the most common of the three types of skin cancer. It is correlated with accumulated exposure, but is more strongly associated with the number of sunburn episodes over the course of a lifetime, particularly childhood sunburns. This is a pattern of intermittent exposure (Armstrong and Kricker 2001). BCC tumors occur on commonly exposed skin, usually on the head. Regularly highly exposed areas like the backs of the hands are rarely affected by BCC, but the occasionally sunburned regions like the trunk are more often affected. It grows invasively but is less likely to metastasize than SCC or melanoma tumors (de Gruijl 1999).
Melanoma is the least common but most deadly form of skin cancer. It grows very aggressively and metastasizes rapidly. Melanoma is not linked to accumulated ultraviolet radiation exposure. It is strongly correlated with infrequent severe sunburns, especially those during childhood. Melanoma’s association with intermittent sun exposure patterns is even stronger than that of BCC (Armstrong and Kricker 2001). Though melanoma often occurs on highly exposed parts of the body, it is distributed more widely than either SCC or BCC (English et al. 1997).
Molecular Causes of Skin Cancer
The overwhelming majority of skin cancer cases are caused by exposure to ultraviolet light. Ultraviolet radiation, especially UVB, is absorbed by DNA. Absorption causes neighboring pyrimidine bases to form either cyclobutane dimers or 6-4 photoproduct dimers. Dimerization changes the base-pairing properties of the DNA strands. If the dimers are not excised and replaced with normal bases before DNA is replicated, the daughter cells may carry mutations at those sites (English et al. 1997). These mutations lead to skin cancer when they affect tumor-suppressor genes such as TP53 in SCC and BCC cells and the INK4A gene in melanomas (Armstrong and Kricker 2001). Loss of tumor-suppressor genes allows the uncontrolled cell growth and division that causes tumor formation.
UVA radiation is much more abundant that UVB. Though UVB is much more effective at causing sunburns, UVA radiation contributes to the formation of skin cancer by suppressing the immune system. Ultraviolet radiation exposure disables the Langerhans cells that take up foreign substances, process antigens, and present them to T-lymphocytes for recognition. This immunosuppression spreads far beyond the exposed skin and may play a role in the growth of melanomas on unexposed sites (Kripke 1988).
Once thought to be “safe UV,” UVA radiation’s role in the development of skin cancer was considered minor when compared to the more intensively studied effects of UVB. However, more recent studies indicate that UVA is much more involved in immune suppression and cancer formation than was first realized (Baron et al. 2003). The immune suppression caused by UVA is thought to protect cells from immune reactions against irradiated skin. These immune reactions against sun-damaged cells cause “sun allergies.” The body avoids these unwanted reactions by decreasing the immune response after high ultraviolet exposure, but this also allows mutated cells to grow more readily and develop into cancers (de Gruijl 1999).
Skin Cancer in Australia
Current information on skin cancer in Australia indicates that one in two Australians will develop a form of skin cancer at some point in their lives. Nearly 300,000 Australians have one or more skin cancers removed in a year, totaling over 720,000 removal operations and over $300 million in health care costs to the Australian Federal Government. The most recent statistical reports state that 3,866 new cases of melanoma alone were diagnosed and 910 people died of the cancer in 1997 (Cancer Council of Victoria 2001) out of a total Australian population of approximately 20 million people. For comparison, in the UK (population approximately 60 million) in 1999, there were about 65,000 cases of skin cancer reported, 6000 of which were melanomas (Cancer Research UK 2003). These data indicate that Australians have a melanoma rate more than double that of their British counterparts.
There are many characteristics of the Australian population that put them at high risk for skin cancer. The continent is mostly populated by light-skinned people of northern European descent, the group at highest risk for skin cancer worldwide. This population is living in a tropical to sub-tropical region of the world with very high ambient levels of ultraviolet radiation. The popularity of sports and other out-door recreational activities in Australia brings people out into the sun frequently, especially during childhood. Physical ideals such as the “healthy tan” are popular in Australia, as in the US. Possibly as a result of heavy influence of European ancestry, many Australians are firm advocates of the importance of getting large amounts of sunlight. However, there is no medical evidence that a suntan improves health (Arthey and Clarke 1995).
Sun exposure is believed to help many conditions such as rashes and neonatal jaundice. Some people still intentionally sun infants, thinking it will help them develop a protective tan or cause the skin to adapt to life in the tropics. Intentional sun exposure, especially for children, greatly increases the risk for skin cancer later in life. Despite the dangers, some health professionals still recommend sun exposure as a treatment for a variety of health problems (Harrison et al. 1999).
One of the biggest problems with childhood sun exposure in Australia is concern about vitamin D production. Vitamin D is produced in the skin when vitamin precursors are photolysed by UVB radiation. Many adults believe that children, especially babies, must be intentionally sunned without ultraviolet protection in order for the body to produce the amounts of vitamin D necessary for proper calcium absorption and healthy bone development. Studies in the late 1980s reported that vitamin D synthesis was suppressed by sunscreen use prompted public health messages that lack of ultraviolet exposure would cause cancer by inducing vitamin D deficiency. However, more recent studies have argued that sunscreen use does not contribute to vitamin D deficiency. Especially in tropical regions of the world, such as Australia, vitamin D requirements can be met easily without deliberate unprotected sun exposure (Marks et at. 1995).
Sun Protection Campaigns
People born in Australia, and those who migrate to the country before age ten, are at a much higher risk of developing skin cancer than people who arrive after age fifteen due to the dramatic correlation between childhood sun exposure and skin cancer risk. Therefore, it is important to emphasize the sun exposure protection message to children and parents. Efforts to increase awareness have utilized flyers, posters, stickers, and activity sheets. These materials are distributed through health care providers, daycare centers, schools, scout groups, swimming programs, libraries, sporting groups, and pharmacies. Survey studies indicate that these efforts have improved the attitude of the public relating to the importance of sun protection (Smith et al. 2002).
Skin protection is now part of health education programs in more than three fourths of schools in Australia (Arthey and Clarke 1995). Some programs also promote school policies such as “no hat, no play” rules that require children to wear sun protection if they will be playing in areas with little or no shade. Efforts are being made to move school recesses and sports to times of day with lower amounts of direct sunlight (Garvin and Eyles 2001). In addition, sun protection messages have been included in various parts of the school curriculum such as science, geography, personal development, and recreation (Marks 1990).
Sun safety programs in Australia are developed by not-for-profit state councils and agencies that combat cancer in general. In 1980, the first sun safety campaign, “Slip! Slop! Slap!”, encouraged people to “slip on a shirt, slop on some sunscreen, and slap on a hat.” The most recent “SunSmart” campaign also provides statistics on skin cancer occurrence and instructions for health care professionals. Along with campaigns aimed at the general population, specific efforts have been made to educate groups such as out-door workers, schoolchildren, parents, and adolescents (Garvin and Eyles 2001).
The Anti-Cancer Council of Victoria runs the “SunSmart” campaign to change the society’s approach to the sun. The campaign was started in 1988 with AUS$1 million from the Victorian Health Promotion Foundation. The program seeks to reduce and control skin cancer by changing personal attitudes and behaviors and bringing about environmental and organizational change. Mass media advertisement campaigns promote sun protection to a variety of population groups. Examples of organizational changes are the accreditation of primary schools as “SunSmart Schools”, based on the inclusion of sun safe practices and education and the adoption of sun protection policies for outdoor staff by local government authorities. SunSmart has also worked with public and private organizations to influence regulations, fashion, building design, pricing of personal sun protection products, and shade structure manufacturing (Montague et al. 2001).
Psychological and social studies have indicated that sunburns and extremely dark tans are beginning to be viewed as “unhealthy” in Australia (Arthey and Clarke 1995). There is now clear evidence that after decades of increase, skin cancer incidence rates are beginning to plateau. Incidence rates in younger groups are dropping, and treatment outcomes are improving due to early detection (Montague et al. 2001). Australia’s continuing efforts to protect the ozone layer and educate the public about sun protection make up an ongoing and evolving success story for this important public health issue.
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