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June 16, 2011

BehindTheMedspeak: U.S. drivers more likely to get skin cancer on left arm than right


The probable culprit: extended exposure to the sun.

Pictured above, the standard mnemonic (ABCD) for melanoma surveillance.

Wrote Jonathan Shorman in a story in USA Today:

New research suggests that people in the USA are more likely to develop skin cancer such as melanoma on the left side of their bodies. Driving may be to blame, because the left arm receives more UV, say researchers from the University of Washington in Seattle, who analyzed cancer cases in a government database.

They found that when skin cancer occurred on one side of the body, 52% of melanoma cases were on the left side. The study provides the strongest evidence to date of a left-side bias in skin cancer cases in the USA.

The National Cancer Institute says that in 2010 more than 68,000 people were diagnosed with melanoma, and 8,700 people died from the disease.

Other research supports the idea that sun exposure while driving can contribute to cancer. In countries where people drive on the opposite side of the road, the right arm gets more sun exposure. A 1986 study cited by the researchers found that Australian men were more likely to show precancerous growths on the right side of their bodies.

Even so, car windows do offer some protection, blocking most UVB rays, an intense form of UV that often causes sunburns.

"The reality is that any of the glass in the car will get out most of the bad UV," says study co-author Paul Nghiem. He adds that UVA rays, though less intense than UVB rays, penetrate glass and can still cause damage to the skin over time.

Nghiem says that for most people who drive with their side window closed, there is no reason to apply sunscreen before driving. But for drivers prone to skin cancer who spend large amounts of time driving, sunscreen may be "prudent," the study says.

"Truckers would certainly be a group who would want to be aware of UV exposure while driving," says Kelly Paulson, a co-author of the University of Washington study. She adds that passengers in a vehicle for long periods of time should also be aware of sun exposure.

Here is the abstract of the paper cited above, published in the December 2010 issue of the Journal of the American Academy of Dermatology.

Increased prevalence of left-sided skin cancers

Background: Previous research has shown an increase in photodamage and precancers on the left side of the face.

Objective: We sought to determine whether there is a higher frequency of skin cancer development on the left side of the body than the right.

Methods: The study was a retrospective review of patients with skin cancer referred to our Mohs micrographic surgery and cutaneous oncology unit in 2004.

Results: When including all types of skin cancers and both sexes, more cancers occurred on the left (52.6%) than the right (47.4%) (P = .059), with a stronger trend in men (P = .042). There were significantly more malignant melanoma in situ on the left (31/42, 74%) than the right (11/42, 26%) (P = .002).

Limitations: Population was comprised of patients referred to an academic medical center and often for Mohs micrographic surgery.

Conclusions: There were significantly more skin cancers on the left than the right side in men. This discrepancy was even more profound in malignant melanoma in situ.

From a letter to the editor of the same journal by the authors of the previously cited study, published in the July 2011 issue: "Our theory regarding the association between asymmetric ultraviolet light and cancer focuses on the head and neck, sites that are exposed in automobile driving and riding."

But before you get too fixated on the logic and truth of these findings, consider the following, from another letter to the editor of the same journal, on the same topic, by a different research group, likewise published in the July 2011 issue:

"Investigations into the laterality of epithelial and melanoma skin cancers are not new. Left-sided excesses of 10% (95% confidence interval [CI], 8-11%) and 15% (95% CI, 5-27%) in the laterality of cutaneous melanoma have recently been evidenced in two concomitantly conducted population-based studies, one being an international comparison and the other a national multicenter analysis of five Swiss regions, respectively. This left-sided excess of melanomas was consistent regardless of vehicle driving on the right (eg, England, Scotland, and Australia) or left (eg, the United States, Finland, The Netherlands, and Switzerland), making asymmetrical sun exposure an unlikely explanation for the laterality of cutaneous melanomas observed in seven countries (my italics). Moreover, automobile driving was unlikely to account for the left-to-right (L/R) tumor ratios greater than 1.00 found for the trunk and the lower limbs, as confirmed in the recent series in the United States.

June 16, 2011 at 04:01 PM | Permalink


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Oh - here's a very special one from Jersey - most specifically, Edison:

American-bound confused desi escaped from Gujerat, house in Jersey, kids learning medicine, now owning property, quite reasonable salary, two uncles visiting, white xenophobic yet zestful.

I can see all of it but the wxyz part.

Posted by: Becs | Jun 17, 2011 5:13:17 PM

Hm, let's see... I'm guessing... telophase, anaphase, metaphase, prophase, interphase? Then kingdom, phylum, class, order, something something, I forgot... I'm not looking this stuff up. Let's see, um, something about pants...stalactites? Stalagmites? No, no, not that... Mad as a hatter, dry as a bone, no, no.... I don't know. Fooey.

Posted by: Flautist | Jun 16, 2011 7:03:48 PM

Interesting Phenomena May Attack Trees. King Philip Came Over From Germany, Stoned. Never Take Tillie's Pants Down, Grandma Might Come Home.

I'll send Joe some of my best Oolong Tea for anybody who decodes all three. Joe can drink or forward it....

Posted by: 6.02*10^23 | Jun 16, 2011 5:47:08 PM

Or a very convenient reason for me to spend the rest of my life in Ireland. Or Scotland. Or England. (Sorry, not interested in Japan, South Africa, etc.)

Posted by: Becs | Jun 16, 2011 5:04:34 PM

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