[The results of a study] showed that when urine from bladder cancer patients was set out among samples from healthy people or those with other diseases, the dogs -- ordinary pets -- were able to identify the cancer urine almost three times more often than would be expected by chance alone.

...

Perhaps the most intriguing finding, though, was in a comparison patient whose urine was used during the training phase.

All the dogs unequivocally identified that urine as a cancer case, even though screening tests before the experiment had shown no cancer.

Doctors conducted more detailed tests on the patient and found a life-threatening tumor in the right kidney.