BMJ  2004;329:1286 (27 November), doi:10.1136/bmj.329.7477.1286

Letter

Olfactory detection of human bladder cancer by dogs

Cause or association?

The first 150 words of the full text of this article appear below.

EDITOR—The study by Willis et al, testing whether dogs can detect signs of bladder cancer in urine, may be the occasion for an amusing cover for the BMJ but this should not be an excuse for relaxing intellectual rigor when assessing the experiment.1 Neither the authors nor the commentator point out that the study design is unable to distinguish cause from association—a basic logical error.

The dogs may be detecting "tumour related volatile compounds" or they may be detecting a substance in the urine that is associated with an increased risk of cancer.

The most obvious candidate would be from cigarette smoking, which would be rather unoriginal, but it could also be other as yet unidentified substances.

Furthermore, while the dogs may only be 41% accurate at detecting urine from people already diagnosed with cancer, the results would also be consistent with a higher accuracy for detecting patients . . . [Full text of this article]

Michael Leahy, senior lecturer medical oncology

Academic Unit of Oncology, St James's University Hospital, Leeds LS9 7TF m.g.leahy@leeds.ac.uk


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Relevant Article

Olfactory detection of human bladder cancer by dogs: proof of principle study
Carolyn M Willis, Susannah M Church, Claire M Guest, W Andrew Cook, Noel McCarthy, Anthea J Bransbury, Martin R T Church, and John C T Church
BMJ 2004 329: 712. [Abstract] [Full Text] [PDF]

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