Sure, technology could probably eventually be developed to diagnose cancer via a patient's breath, but it turns out that dogs can do it naturally.
German scientists tested two German shepherds, a Labrador retriever, and an Australian shepherd. Each dog sniffed the breath of 220 patients, correctly identifying lung cancer at a rate of 71 percent. They also ruled out cancer in 372 out of 400 samples.
Other research has shown that dogs have had some success at identifying bladder cancer, colon cancer, breast cancer and have detected low blood sugar in diabetics.