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Sunday, October 4, 2009

The great screening disappointment

There were two stories which hit the lay press this week which dealt with related issues, prostate cancer and melanoma. The NY Times article - Melanoma on the Rise, or Is It Just Diagnoses? By NICHOLAS BAKALAR September 28, 2009 ) is in fact one of series articles in the NYT dating back over 10 years which have raised similar questions after prompting from articles published in the peer-reviewed medical literature.

This article, reporting on a study published in the September issue of The British Journal of Dermatology, raised the question whether early screening using skin exams actually results in any patient benefit. The usual actors weigh in, stating the usual justifications for their positions, an exercise which I think is the equivalent of what we used to observe in our very small children when they engaged in "parallel play". They were in the same room and using the same toys, but they displayed little actual substantial interactions or exchange.

The realization that what appeared to be such a simple concept, that is screening for cancer, turns out to be so devilishly difficult is slowly playing out in the peer reviewed realm and inexorably spilling into the lay press. The history of the screening paradigm is wonderfully reviewed by Dr. Barnett Kramer (Editor of the JCNI) in a great video on the Research Channel.

It can be accessed via Google video. The take home message is it is easy to discover what can be diagnosed as early cancer. Whether what is discovered is actually biologically malignant and whether intervention prolongs lives is uncertain.

There are some very interesting parallels to earlier events in human history outside of medicine. Many has always had a desire to predict and control future events. Throughout much of history, these efforts have focused on supernatural deities and magical thinking. For over 1000 years the Oracle at Delphi held sway over critical decision making in the western world. The same origins of hard science in astronomy are intermixed with the magical thinking in astrology. The revolution of science and Newtonian mechanics led earlier generations of scientists to believe in determinism; that with enough information regarding our current state we could predict the future.

The quantum revolution of the early 20th century put an end to such thinking in the world of physics and the impact of this is still diffusing out, slowly influencing thinking in other predictive realms. It is unquestionably painful to the luminaries of both physical biological sciences, creating and understanding of the uncertainty which is inherent in any predictive activity. The hard lesson was that one can never be sufficiently informed about the present state to reliably predict the future state. Determinism is dead and this should be recognized as being true within medical sciences as any other branch of science.

Predictive health initiatives and screening activities to prevent future events are wonderful marketing tools. We all want them to be true, they attract idea patients (who are not sick), and they validate our own desires to have predictive powers. Like other fields (e.g - finance, meteorology, business) the value of health professionals is still linked to our ability to look into the future and we are understandably reticent to admit the limits of our prognisticatory capabilities. If we can't provide such information, where is our worth?

The problem with the predicting the future is that it has not happened yet. Where the stakes are high enough, prediction will always result in action which always has the potential to alter the outcomes. Whether the intervention made a difference is not discernible. It is Schrodinger's cat all over again.

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