Monday, January 09, 2006

Replication vs. Precautionary Principle

Superfluous Medical Studies Called Into Question

By David Brown
Washington Post Staff Writer
Monday, January 2, 2006; Page A06

In medical research, nobody is convinced by a single experiment.

A finding has to be reproducible to be believable. Only if different scientists in different places do the same study and get the same outcomes can physicians have confidence the finding is actually true. Only then is it ready to be put into clinical practice.

Nevertheless, one of medicine's most overlooked problems is the fact that some questions keep being asked over and over. Repeated tests of the same diagnostic study or treatment are a waste -- of time and money, and of volunteers' trust and self-sacrifice. Unnecessary clinical trials may also cost lives.

All this is leading some experts to ask a new question: "What part of 'yes' don't doctors understand?"



BrooklynDodger Comments: Let's apply this principle to public health and carcinogen classification.

The current IARC rules require two separate bioassays [in the absence of other evidence] to call a chemical a 2b "possibly carcinogenic to humans." For example, diethanolamine caused increased liver tumors in male and female mice when applied to the skin, but no tumors in rats. Yet, because these separate experiments were done at the same time in the same NTP bioassay, the Working Group called the male and female mice one study, the evidence limited, and the chemical "not classifiable." The majority of the working group which voted inadequate included those who interpreted the rules narrowly [and incorrectly in the Dodger's opinion] and a faction that doesn't believe mouse liver tumors predict human cancer risk, even in female mice.

IARC (2000) Diethanolamine. IARC Monogr Eval Carcinog Risks Hum 77, 349-79.

The Catch-22 is that "everyone" knows that an NTP bioassay done under GLP will produce the same result every time. [Had rats shown an association, they might have bought that as a second study.] So there's no reason to do the second study. [Actually, it's really been done, where the dieathanolamide-fatty acid condensation products, and triethanolamine are carcinogenic in proportion to diethanolamine contamination.] So DEA is in IARC limbo for ever.

Which means that a proper risk assessment for the amount you absorbed from skin lotion with traces of DEA contaminant won't ever be done. Rest assured, there is a growing body of "mechanistic" data to support a Houdini risk assessment should this ever move forward.


The Dodger will return to the WaPo article in another post.

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