In the late 1980s in the UK, a border collie-Doberman mix began paying extreme attention to a mole on his owner’s left thigh. The 44-year-old woman noticed that the dog would sniff there for minutes on end, trying to bite it off whenever she wore shorts.

The dog’s fixation wasn’t random. What the dog was smelling wasn’t just the mole, but the melanoma causing it — and its subsequent removal might just have saved the woman’s life.

In this new book, author Horowitz shows how canines, whose sense of smell is anywhere between 10,000 and 100,000 times more acute than ours, might turn out to be an essential weapon in the fight against cancer and other diseases.

The British woman in the book, who isn’t named, is just one of several examples Horowitz gives on how dogs smelled cancer before doctors diagnosed it.

The scientific research on this is still in early stages, but Horowitz quotes the medical journal The Lancet, which states: “Perhaps malignant tumors such as melanoma, with their aberrant protein synthesis, emit unique odors which, though undetectable to man, are easily detected by dogs.”

Horowitz notes that smell was used by doctors as a diagnostic tool “for thousands of years,” a practice that stopped only recently.

“Smelling one’s patient and his diseases goes back at least to Hippocrates, who advised doctors to keep an ‘open nose,’ ” Horowitz writes. The ancient greek physician Galen “warned people to avoid ‘those who exhale such putrid humours that the houses in which they lie in bed become stinky.’”

In the 18th century, knowing how smells related to disease became a medical specialty, with “a sweet smell of onions indicating smallpox; fresh baked bread . . . typhoid; the smell of a butcher’s shop . . . a sign of yellow fever.”

But as modern medicine successfully tackled infections (“and their pungent odors”), smell disappeared from the doctor’s tool kit.

If dogs can revive the use of smell for diagnostic purposes and make it more effective than ever, the results for modern medicine could be substantial.

“The standard business of cancer detection [is] expensive, lengthy, and sometimes painful,” Horowitz writes. “The hope of replacing office visits, biopsies, and CAT scans with a dog scan, so to speak, [is] irresistible.”

Now some are working to bring it back, but this time with dogs on the front lines.

Horowitz takes us into a canine training center in Philadelphia where dogs are presented with plasma samples from patients sick and healthy and given treats when they sniff out the cancer. In time, they improve, finding the disease at rates far greater than chance would allow.

And it’s not just cancer they can detect.

‘The hope of replacing office visits, biopsies, and CAT scans with a dog scan, so to speak, [is] irresistible.’ - Alexandra Horowitz, author

“Work is well under way training dogs in detecting hypoglycemic and hyperglycemic episodes (in diabetics) as well as in alerting prior to an owner’s epileptic seizures,” Horowitz writes.

“One research paper describes dogs, glowingly, as a ‘fully biocompatible and patient-friendly alarm system’ for hypoglycemia.”

The first report on the success of diabetic-alert pooches came out in the UK in 2013 and found that subjects reported “pet dogs spontaneously responding to their hypoglycemic episodes.”

For proof, researchers asked some diabetic dog owners “to take blood glucose samples and note when they believed their dog alerted — by nuzzling, pawing, even retrieving the blood-test kit. It turned out that the times when these dogs alerted was more likely to be out of the desirable blood-sugar range than the other routine sample times.”

In these cases, it’s still unclear exactly what the dogs are reacting to, although there are several theories.

“Dogs might have been smelling a change in their owners’ sweat or even breath,” writes Horowitz, “but also, as acute observers of their people, might have been noticing some change in behavior that served as corroboration.”

We don’t yet know how big an impact dogs can have on disease diagnosis and prevention. But Horowitz shows that medical science could be ignoring one of our most potentially valuable life-saving tools.

“Except for the strangeness of dogs wagging into the medical arena,” she writes, “there [is] no reason that dogs [shouldn’t] be able to become diagnosticians.”