Adjusting for Risk: Skin Cancer
Between 40 and 50% of Americans that live until 65 will have a basal cell carcinoma or a squamous cell carcinoma.1 I know--yawn--can I get some sunscreen on the side with that statistic? We've been inundated with so many statistics like this, and many of us just shrug at it, but should we?
Damn Lies and Statistics
The phrase goes, there are three kinds of lies: Lies, damn lies, and statistics. We've become familiar with clever and misleading manipulation of numbers to support otherwise weak or meritless positions in politics, business, or academia. As misleading or “framing” statistics have become all too common, the public has become much more skeptical about statistics in general. Statistics, when used properly can provide important and relevant information to guide good decision making.
Famed evolutionary biologist, Stephen Jay Gould wrote a short essay with the title, “The Median isn't the Message” when he was diagnosed with mesothelioma in 1982. Mesothelioma is a relatively rare cancer, mostly associated with asbestos exposure, and one that has a poor prognosis--with a median survival rate of 8 months after diagnosis.2 This was understandably devastating news--and in Dr. Gould's account, the medical team discouraged him from researching his condition so that he wouldn't be disheartened. With his training in the sciences, he was able to understand what the median statistic didn't capture--that the other 50% who survive may live much longer than 8 months, and that the median isn't an average. Indeed, Dr. Gould recovers from this cancer, and lives for another 20 years in which has produced his most important works. This short essay still continues to inspire and give hope to patients, but it also provides an important lesson about interpreting statistics in general--that risk is individual in a way that general statistics often don't capture well. In Stephen Jay Gould's case, there were many factors that made him more likely to be a survivor than not--he was relatively young, had been diagnosed early, and had access to great medical care, factors which made him more likely to be in the survivor group who live longer than 8 months, and not only that, but have an expectation to live much longer than that.3 While the median survival rate may have been bleak, due to his training in science, Dr. Gould was able to see the light in the darkness--that median isn't a description of how long he is likely to live.
A lot of people have a misconception that risk is flat across all population at all ages, and as we can see with Stephen Jay Gould's case, that's simply not true. Risk factors are individual, and constantly change over time. To take an extreme example, if you are a 75 year old man, you probably shouldn't spend your entire retirement savings this year on the assumption that you'll live until the average life expectancy of a male--76. There are many obvious reasons why this isn't a great idea, even if you believed that dying with any money to your name constitutes poor life and resource management. Statistically, a male's life expectancy might be 76, but if you are 75 and male, your current expectation is not to die within a year; it's to live until age 86.4 Like Dr. Gould's case, individual factors matter, and the fact that you already lived to 75 is very relevant. Individual circumstances also matter very much--if you are in horrible health at 75 and committed to spending all of your money before death, you might want to start spending, but if you are 75 and have no health problems, are happy, and live a healthy lifestyle, this is also relevant information that skews you towards living longer. The reverse is also true, and often more relevant in terms of decision making. Various factors can make you a part of a higher risk population, and have practical consequences on how you should view risk.
Adjusting for Skin Cancer Risk
Getting back to skin cancer, it's scary enough that nearly half of Americans will get a skin cancer by the time that they're 65. This is reason enough to take steps to avoid over-exposure to the sun. If, however, you are in a high risk category, this can skew your odds enough to fundamentally change how you should think about the risk of skin cancer. If you are 20 and have dark skin and no family history of skin cancer, although there will always be a non-zero chance that you develop skin cancer, it's probably not practical to have your skin checked every 3 months by a dermatologist. If you are a transplant patient in your 60s, and have had skin cancer in the past, that precaution should practically be mandatory because your risk is incomparably high compared to the 20 year old. These are some skin cancer risk factors that you should be aware of, and adjust for:
Lighter Skin Tone: People with lighter skin tones are more susceptible to skin cancer compared to people with a darker skin tone. Melanin provides a natural sun protection factor (SPF) and the difference is evident after decades of accumulated sun exposure from both skin cancer rates, as well as studies on other signs of UV-related aging. Skin cancer is a much greater threat for people with lighter skin tones.5
Age: The incidence of skin cancer (and all cancers) increases with age. The body is both more susceptible to cancerous mutations and less efficient at clearing changes through cell death, and the skin has also been exposed to sun damage for longer. Risk is not distributed equally. As an older individual you are at higher risk compared to younger people, and frequent check-ups are always a good idea, especially if other risk factors also apply.
Sun Exposure: Lifestyle matters. If you spent a weekend at a Mexican resort, and had a mild burn, it's probably not a big deal. People who regularly enjoy tanning or are careless about sun protection are clearly at higher risk compared to the average person. One of the biggest risk factors that isn't talked about enough is occupational risk. If you regularly work outdoors as a construction worker, your total exposure is probably higher than many hard-core sun tanners. The point isn't to quit your job (if only) but to be aware of the heightened risk factor, as a high risk group, and to take sun protection more seriously than most. For example, you should be going for check-ups regularly.
Actinic Keratosis and other warning signs: Actinic keratosis is considered a pre-cancer. Treatment is recommended due to the risk of these lesions turning into a skin cancer called squamous cell carcinoma. The chances of this occurring are somewhere from less than 1% to 20% depending on how the statistics are taken.6 The important message here isn't about how “scary or likely” that number seems. What's important is that actinic keratosis is unequivocal evidence that the skin in the area has taken significant damage from accumulated sun exposure, and puts you at significantly higher risk not only of the AK turning into cancer, but of developing a skin cancer independently.
Previous Skin Cancer: Like actinic keratosis, the fact that you had skin cancer is evidence of existing damage, so you are in fact, at high risk. Remember that not all damage is visible on the surface of the skin, and removing a skin cancer does not remove all the sun damage that your skin has had. What you can visually see is often just the tip of the iceberg. Treating or removing skin cancer doesn't reverse the damage that's already there. If you know that certain risk factors apply to you, it's very important that you take this seriously, and to adjust your expectations. Sun protection is important for everyone, as it also causes noticeable and very visible symptoms of premature aging (wrinkles, hyperpigmentation, fine lines, crepey skin, poor elasticity), but it's especially important for people who are at high risk. Regular check-ups, and strict sun protection is critical if you are in a high risk category.
Organ Transplant Patients: Organ transplant patients are approximately 100 times more likely to develop squamous cell carcinomas compared to the general public.7 These patients should be doing check-ups very regularly.
2This was in 1982, but to this day, it is still a serious cancer with a bleak overall prognosis.
3A common pitfall is assuming that most people would die somewhere between 6 and 10 months, and that abnormalities like Stephen Jay Gould's case is exceedingly rare, like standard deviation in normal distributions. Right skews like this are not uncommon.
4If you make it to 86, 91 is your new “expectation.” That is, the fact that you've lived that long is most certainly relevant data.
5For people with darker skin tones, even though the risk of skin cancer is significantly lowered, the risk of hyperpigmentation (dark spots and patches that contrast with surrounding skin) is much higher. Sun protection is important for everyone.
61% and 20% is a large variation and suggests that the methodologies used vary considerably from study to study. What's clear is that the risk is real, and actinic keratosis should not be ignored, and a doctor should be consulted.