As summer beckons, we should take a moment to focus on the sun's dark side. The source of all life on Earth, the sun is also a fountain of environmental carcinogens. Specifically, we now know that the sun's ultraviolet radiation is the primary cause of most skin cancers.
Skin cancer, long thought to be a disease of little public health significance, has now become epidemic. An estimated 90,000 new cases of malignant melanoma and well over one million cases of non-melanoma skin cancer will occur in the United States this year. Melanoma will cause 8,000 deaths, and non-melanoma skin cancer will kill another 2,000. Melanoma is now the most common cancer in women aged 24 to 35. Once a disease of men in their fifties and sixties, it is not unusual for women in their twenties to develop basal cell cancer or squamous cell cancer.
While the incidence of skin cancer has risen dramatically, so has our understanding of its causes. For over fifty years, ultraviolet radiation from the sun has been the number one suspected cause of skin cancer. Epidemiologic data from Australia, animal studies with artificial sources of ultraviolet light, and the development of skin cancer in individuals with a genetic inability to correct the DNA damage caused by ultraviolet radiation provided circumstantial evidence of the connection. Recent work has made the causal link between the sun and skin cancer at the molecular and cellular level.
Ultraviolet radiation causes specific and unique mutations in the tumor suppressor gene that produces a protein called p53. This protein is involved in a process called apoptosis in which damaged cells commit "suicide" to ensure that their defective genes are not passed on to daughter cells. (This is perhaps the first indication that self-sacrifice may be an intrinsic human trait!) Damaged by the sun, but not quite able to commit suicide, the mutated cell continues to proliferate at the expense of normal surrounding cells, resulting in a pre-cancerous growth that can progress to a full-blown squamous cell carcinoma.
But how should we communicate to people about skin cancer and its prevention? If our key message is "stay out of the sun forever," we are doomed to fail. Creating a culture of cave dwellers is no way to decrease the incidence of skin cancer.
Moreover, in educating the public we confront formidable forces: cultural icons who are as bronze as the statuary in the Louvre, the sheer pleasure of being in the sun, and the perceived incremental health benefits of ultraviolet radiation. The dearth of pale actors, actresses, corporate leaders, and politicians confirms that a tan is identified with health, wealth, and power, rather than the travails of the working class, as in the past.
The artificial tanning industry promises that ultraviolet radiation from their machines causes less damage than natural sunlight. But in both cases, a tan is the body's response to injury. Microscopic pigment granules produced by skin pigment cells aggregate around the cell's nucleus to shield the DNA from the marauding rays and prevent mutation. It is irrelevant whether the ultraviolet radiation came from a bulb or a star.
Whether natural or artificial, ultraviolet radiation causes the skin to age prematurely. The inescapable irony is that teenagers and young women pursue a tan to look more attractive, but trade a moment or two of sunny radiance for a whole lifetime of premature wrinkles, fine lines, and haggard-looking skin. As young people consider themselves immortal, not even appeals to lifelong vanity, let alone warnings about cancer, are sufficient to deter them from the tanning booths.
But the difficulties of educating the public about the causes of skin cancer do not diminish our obligation to try. There are enough other diseases about which we do not have a clue as to the cause. With skin cancer, we know very well how we can prevent it - and prevention is always easier than treatment.
A good place to start is to ensure that the public has access to accurate information. While pseudoscience and the anti-aging industry represent an important source of potential misinformation, the Internet often provides damaging false information as well. Amazingly, the Internet has the same level of credibility with the patient as television does with the consumer: "I read it on the Web, so it must be true."
At the same time, tanning parlors should be regulated. While barbers, hairdressers, taxi drivers, bar owners, and doctors are often licensed, permits are rarely required to operate a tanning parlor. None of the other professions listed above, however, knowingly exposes its clients to a confirmed environmental carcinogen. Until the tanning industry chooses to police itself, customers should eschew the bulbs and pursue the spray: wear an artificial tan.
This preventable disease should be the focus of a comprehensive educational campaign similar to anti-smoking campaigns, which are now bearing fruit in many countries. In addition, scientific research on this most accessible of human organs will continue to identify innovative treatments and modes of prevention, which may well become applicable to other cancers.