As early as the late 1980s, scientists proposed that dogs could detect malignant tumors through smell. Since then, dogs have taken on another task—helping doctors identify cancer patients. However, many people have voiced doubts—why should dogs be able to smell the scent of cancer patients?

       We all know dogs have an extremely sensitive sense of smell, but many people might have no idea how sensitive it actually is. Simply put, dogs can distinguish 2 million different scent concentrations, which is unimaginable for humans. Moreover, dogs perceive scents on a molecular level—for example, if a teaspoon of salt is added to 500 kg of water, a dog can sniff it out easily, can you?

       Scientists say that the scent of cancer patients differs from that of healthy people because tumors produce some volatile substances. Although humans cannot detect this odor by smell, dogs absolutely can, and trained dogs have a very high accuracy rate in their judgments. Recent studies show dogs can identify bladder cancer patients by smelling urine, detect lung cancer patients by smelling exhaled breath, identify colorectal cancer patients by smelling feces, and so on, with an accuracy rate as high as 90%.

       If dogs could really enter hospitals as "dog doctors," this would bring many conveniences to both doctors and patients. For example, to determine whether suspected patients have colorectal cancer, these patients currently need multiple colonoscopies, which cause strong discomfort. But letting dogs diagnose by scent would cause no pain for those being examined and would make the process much simpler.

       Nonetheless, despite this, many people say that if one day they need cancer screening at a hospital, they would certainly choose to trust the data from medical instruments rather than letting dogs sniff once and make a conclusion.