It is well known that the key to effective treatment of cancer in humans is largely the rapid diagnosis of the disease. However, in the early stages, oncological diseases do not cause specific clinical symptoms, and for their timely detection, it is necessary to carry out screening aimed at identifying tumor markers, pathological cells, minimal radiological changes, etc.. In this case, of course, finding a simple, reliable and inexpensive examination method is of great practical importance. One of the promising areas of screening is the identification of traces of certain chemical compounds produced by cancer cells. Indirect confirmation of the effectiveness of this approach is the work that has demonstrated the ability of specially trained dogs to smell the odors of patients with lung, bladder or colon cancer.

Modern diagnostic methods, such as annual computed tomography (CT) of the thoracic organs of malicious smokers at high risk of developing lung cancer, reduce the risk of death from this condition by 20%. However, false positive CT results are seen in approximately one in four patients examined, which leads to the need for additional invasive examinations.

In a publication published in the European Respiratory Journal in August 2011 (European Respiratory Journal), German researchers claim that specially trained dogs can sense human lung cancer with rates of sensitivity fairly high and specific. In the study, specially trained dogs (two German shepherds, an Australian shepherd and a Labrador retriever) correctly detected the presence of lung cancer by smell in 71 cases out of 100 samples of exhaled air from patients with lung cancer. In addition, they correctly excluded lung cancer in 372 of the 400 patients without this disease, that is, the false positive rate was only about 7%. Thus, the results demonstrated by dogs have proven to be better than CT and bronchoscopy combined.

Earlier in the literature, cases have been described repeatedly when dogs have clearly told their owners that they have undiagnosed skin, breast or lung cancer, stubbornly sniffing or scratching the affected area. In addition, dogs whose owners suffered from type 1 diabetes mellitus were specially trained to detect low levels of glucose in their blood by smell to prevent the development of severe hypoglycemia.

Previous studies on the ability of dogs to detect cancer by smell have shown mixed results. Thus, in a study whose results were presented in 2004 in the British Medical Journal (Willis CM, et al. BMJ.2004; 329 (7468): 712), dogs correctly diagnosed a bladder cancer at 40 years of age. % of cases, whose reliability is lower than existing laboratory screening methods, but clearly exceeds the rate of 14%, which can be expected by random selection.

In a study by Japanese scientists, it has been shown that dogs can detect the presence of colon cancer by the smell of exhaled air samples and stool with 90% accuracy, which is almost as effective as colonoscopy.

Undoubtedly, in studies with dogs, the individual abilities of each "diagnostician" are of great importance, as well as the duration and quality of the animal's training. In a study of German scientists, dogs were trained for 9 months, in other studies, dogs were only trained for 3 weeks. In addition, it may be important to know which samples are used for testing (exhaled air, blood, urine, etc.).

In a study by Ehmann et al. (Ehmann R, et al. Eur Respir J. 2011) involved 220 volunteers (110 in good health, 60 lung cancer patients and 50 COPD patients). Study participants exhaled through a glass tube filled with fleece. The tubes were labeled and mixed, so that neither the dog owners nor two independent observers could know which of the samples belonged to a healthy person and which patient had lung cancer. The dogs were presented with 5 samples at a time, while one of them belonged to a patient with lung cancer. As a result, dogs with high accuracy (71%) determined samples obtained from patients with lung cancer, including patients in the early stages of this disease. It is important that the accuracy of the determination of lung cancer in dogs has not been affected by the smell of tobacco or food taken by volunteers.

Researchers believe that dogs are able to accurately capture and recognize volatile organic compounds (VOCs), the combination of which constitutes the so-called "chemical portrait" of the body. In nature, there are many VOCs, for example, only in the air exhaled by a person more than 4,000 are identified. Scientists say dogs' ability to smell is developed 100 to 1,000 times better than humans. But not only is the sensitivity of the olfactory receptors important, but also the ability of dogs to analyze VOC spectra and identify those that correspond to a particular type of cancer. Therefore, the main objective of the scientists is not to use dogs for the diagnosis of cancer, but to create an automatic analyzer capable of capturing and recognizing spectra of specific “cancerous” smells according to the principle of “ dog nose 'to perform screening tests for human oncopathology.