Tuesday, July 10, 2007

Turtles, Birds and Bears

Dermatologists in the U.S. spend a fair bit of time screening patients for skin cancers. In spite of this, there is little evidence that this screening decreases the mortality from skin cancer (mainly melanoma).

"Cancers follow three basic patterns: turtles, birds and bears.
1. Turtles move so slowly that you can still capture them while they’re moving slowly along;
2. The birds fly away so quickly that you can’t catch them in time;
3. The bears can escape if you ignore them, but if you catch them in time, you can capture them."

This simple but brilliant formula comes from a superb article by Christie Aschwanden on sunscreens and skin cancer that appeared in the July 10, NY Times.

Doctors Balk at Cancer Ad, Citing Lack of Evidence See Permalink.

This is a reasoned piece which quotes the best evidence-based information we have. Please read the article and draw your own conclusions.


  1. The inference that skin cancer screening and detecting many melanomas in situ may not ultimately make any difference to melanoma mortality rates is counter intuitive. I appreciate that the melanomas that kill you are mainly amelanotic and nodular lesions arising on the back and being ignored untill they are too thick. Some would argue these are the birds that have already flown and may have flown very early in the piece but we have to assume that is not the case and keep up our attempt to diagnose and remove these lesions very early because it will statistically take some time before the truth of this approach is verified. The question is statistically how long will it take? Anyone able to answer that?
    I think you are a bit hard on the AAD and the Cancer Society David!

  2. Greetings from "down under".

    My practice is in a sunny coastal resort area in Australia. Each year over the last 4 years in a relatively stable practice population I have performed about 4000 skin examinations for skin cancer, finding about 70 melanomas/year (and umpteen more SCC & BCC's), of which only 15% (about 11/year) are invasive, and the majority of those <1 mm Breslow. Most of the lesions were unknown to the patients, and the majority of the melanoma-in-situ was lentigo maligna (i.e. on grossly sun damaged skin). There has been only one "bird" in that time.

    To me it seems then that about 40 "bears" have been captured by skin examination, an unknown number of in situ lesions that were imminent "bears" were stopped in their tracks and a large number (about 1200/year) of non-melanoma skin cancers were able to be treated by rather conservative methods (thus reducing significant morbidity).

    The validity of a public health program like this rests very much on the latitude at which it is conducted and population incidence of the target disease - thus the comments made by Drs Kramer et al may be quite valid for Boston but not quite so for, say Florida....and definitely not for northern Australia!


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