Ask Marilyn
How Well Can Dogs Detect Cancer?
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If certain dogs can be trained to detect cancer in humans with a high rate of success, why aren’t they used more regularly?
—Alan Stevens, Ipswich, Massachusetts
When tested with known samples, dogs are great at telling which are cancerous. But that’s not helpful. Dogs would need to be great at screening: telling when a sample is not cancerous. That’s different. False positives are bad enough, but false negatives are far worse. (People who do have cancer would believe they do not.) When dogs were tested in a setting more like a screening, they didn’t do well enough: Nearly one in four samples were false negatives, meaning that 25 percent of the cancers were missed.
