Can Dogs Smell Cancer?

Yes, dogs can smell cancer. They can even smell it “in situ”, or at stage zero.
Let’s take a closer look at why dogs are even interested in smelling cancer in the first place. Why would a dog be interested in smelling cancer? There has to be something in it for them. Dogs have lived side by side, co-evolving with man for well over 100,000 years. Man provided shelter and food for the dog (and early wolf), and in turn, the dog warned man against impeding danger, pointed towards prey and food, and eventually guarded our livestock and crops. We provided for the dog, and the dog used his nose to help provide for, and protect, us. The key here is that the dog used his nose for our benefit. Top dog and wolf evolutionists and biologists are now saying that man may have never made it past the agricultural stage without the dog (and his nose).
So why would a dog want to smell cancer? The answer is simple: if something is wrong with us, this will affect the dog. If we are sick, this could directly affect our ability to provide food and shelter for the dog. The dog “notices” small changes which could signify that we are in trouble. For example: if I have a cut on my leg, under my jeans and socks, why does almost every dog find and sniff the cut? They are noticing a change, or something different, that’s not like the rest of us. This small change can mean that we may become incapacitated in some way, which means the dog may suffer. Most prey animals which get caught and killed by predators are sick or injured in some way. The slowest, or sickest bird gets caught. Imagine the years of a dog learning to find the “sick” scent. Or better yet, the dog is “reinforced” (eating the sick bird) by having the sick scent paired with the eating of the bird. Smelling disease helps the dog catch his own prey, as well as larger prey for man. The sick scent is very important for the dogs (and mans) survival.
Dogs can smell in parts per trillion. An example of this is: one cc (less than a drop) of blood, diluted into 20 olympic sized swimming pools. The dog can smell with ease that there’s blood in the pool. Another example: 3 seconds in 100,000 years. Dogs smell like we see. We walk into a room and see the room; a dogs walks into the room and smells the room. We see a cut on our leg; the dog smells it. We have trained dogs to sniff gun powder, narcotics, missing persons, and now, finally, diseases. The interesting part about this is that cancer absolutely has a smell. Most oncologists will tell you that humans can actually smell cancer in latter stages through the patients breath. If we can smell it at stage 3-4, then of course a dog would be able to detect the scent much earlier, in stage 0, 1 or 2. There are many published studies that prove dogs can detect cancer through breath samples, and scientists and doctors are trying to come up with a breathalyzer test that works as good as the dogs nose. So far, the only ones that can smell cancer in early stages, are the dogs. See Diagnostic Accuracy of Canine Scent Detection in Early and Late Stage Lung and Breast Cancers (Integrative Cancer Therapies (March 2006, Vol 5, No 1)
Training dogs to smell cancer is done in the same way that bomb and narcotics dogs are trained, pairing the target odor with a high value reward. (Kind of like the dog smelling the sick bird, and then getting to eat it). With breath, however, things can get a little tricky. Remember, drugs and gun powder can be isolated, but
“cancer scent” is one of the thousands of organic compounds within a humans breath. In order for the dogs to generalize the “cancer scent”, many samples with the common odor must be used. Also, the dogs must be trained to ignore healthy breath, and all other breath with diseases other than cancer. This means samples. LOTS of samples to use for the dogs training. Cancer samples, disease controls and healthy controls are needed, and the order and specifics of the introduction of cancer through latter stage training is extremely specific, in order for the dog to generalize the cancer scent. Right now, the important thing to remember is that dogs can smell cancer. They have good reason to, and it can save your life.

From: http://dogsdetectcancer.org/can-dogs-smell-cancer/