A Labrador retriever trained in cancer scent detection achieved 95% accuracy when testing exhaled breath samples and 98% accuracy for stool samples taken from patients with colorectal cancer (CRC), reports a Japanese study in the journal “Gut”.

The faecal occult blood test (FOBT) is currently the most economic and non-invasive screening method for CRC. However, the positive predictive value of FOBT for CRC is approximately 10 %, indicating a need for the development of novel more effective CRC screening methods. Previous studies have reported canine olfactory detection of melanoma as well as bladder, lung, breast and ovarian cancer.  Furthermore, in the exhaled breath of patients with lung and breast cancer several volatile organic compounds have been identified as candidate substances for early detection of cancer using gas chromatography/mass spectroscopy.

In the current study, Hideto Sonoda, and colleagues from Kyushu University (Fukuoka, Japan) set out to investigate whether canine scent detection might be an effective tool in CRC screening.

In the study exhaled breath samples (acquired from the beginning to the end of exhalation) and watery stool samples were obtained from patients with CRC and from healthy controls. Each test group consisted of one sample from a patient with CRC and four control samples taken from volunteers without cancer.  Cancer detection was undertaken by a specially trained 8-year old female black Labrador who had been trained at the St Sugar Cancer Sniffing Dog Training Centre (Chiba, Japan). Training involved a reward-based approach where correct identification of cancer samples was rewarded by play with a tennis ball. The dog - who could already detect 12 types of cancer in patients’ breath samples before she joined the colorectal study - had been trained to indicate cancer by sitting down in front of the station containing the cancer sample. The identity of the samples was blinded to the dog, the handler and the laboratory assistants, thereby making the study double-blind.

Results show that when five samples of either breath or stool were presented to the dog, only one of which was cancerous, she was able to choose correctly in 33 out of 36 breath tests and 37 out of 38 stool tests. Furthermore, the study showed that the canine scent judgement was not confounded by current smoking habits, benign colorectal polyps, inflammation or infection.

It may be difficult to introduce canine scent judgement into clinical practice, write the authors, owing to the expense and time required for the dog trainer and for dog education. “It is therefore necessary to identify the cancer-specific VOCs detected by dogs and to develop an early cancer detection sensor that can be substituted for canine scent judgement,” conclude the authors.

One limitation of the study is that the dog did not reliably recognize any abnormal scent from precancerous polyps. In contrast, tests such as colonoscopy can accurately recognize these polyps, thereby enabling them to be removed in order to prevent colon cancer before it is fully developed.

Reference

H Sonoda, S Kohnoe, T Yamazato, et al. Colorectal cancer screening with odour material by canine scent detection.  Gut doi:10.1136/gut.2010.218305