Elsevier

Journal of Veterinary Behavior

Volume 5, Issue 3, May–June 2010, Pages 145-152
Journal of Veterinary Behavior

Review
Canine scent detection of human cancers: A review of methods and accuracy

https://doi.org/10.1016/j.jveb.2010.01.002Get rights and content

Abstract

Early detection of cancers, although essential for treatment effectiveness, can be difficult to achieve, and some tests introduce additional health risks. New, non-invasive detection methods with greater sensitivity and specificity are needed. Several authors have published research suggesting that dogs may be able to detect lung, breast, prostate, ovarian, and melanoma cancers by smelling skin lesions, urine, exhaled breath, and surgically extracted tumors. We conducted a systematic search using the PubMed and EMBASE databases to identify all known published data on canine scent detection of cancers. Of 531 potentially relevant publications, 11 full text articles were examined, and 5 were selected for inclusion in the review. Two studies involved dogs detecting breast cancer (sensitivity 88% using exhaled breath and 22% using urine; specificity was 98% and 20%, respectively), 1 involved bladder cancer (41% of urine samples detected), 1 involved melanoma (75–85.7% of in situ tumors detected), 1 involved lung cancer (sensitivity 99% and specificity 99% using exhaled breath), 1 involved ovarian cancer (sensitivity 100% and specificity 97.5% using thawed frozen tumor samples), and 1 involved prostate cancer (18% of urine samples detected). One study on ovarian cancer is in progress. Early successes with canine scent detection suggest chemical analysis of exhaled breath may be a valid method for cancer detection. Tests using exhaled breath showed better sensitivity and specificity than with urine. Future research should target other tumor types, and seek to identify what exhaled compounds may signal a cancer diagnosis.

Introduction

Initial interest in the hypothesis that dogs might be able to detect cancer in humans began in 1989 when Williams and Pembroke sent a letter to The Lancet in which they described a case where a woman was encouraged to get a skin lesion examined by a dog, who showed an inordinate amount of interest in the spot on her skin (Williams and Pembroke, 1989). After clinical examination, the lesion proved to be a malignant melanoma. Several similar cases have been reported since then. Pickel et al. (2004) and Willis et al. (2004) published papers indicating that the hypothesis suggested by Williams and Pembroke might be valid. To date, studies have been published on the detection of bladder (Willis et al., 2004), lung (McCulloch et al., 2006), breast (McCulloch et al., 2006), prostate (Gordon et al., 2008), ovarian (Horvath et al., 2008), and melanoma (Williams and Pembroke, 1989, Pickel et al., 2004) cancers using a dog's sense of smell.

Early detection of many cancers, although essential for treatment effectiveness, can be both difficult to achieve and introduce new health risks. High-resolution scanning technologies such as CT, MRI and PET are highly accurate, but are costly and carry the risk of unnecessary biopsies for benign lesions (Jett, 2005). CT scans also increase radiation exposure, which could increase the risk of cancer over a period of several decades of use in screening (Martin and Semelka, 2006). Low-resolution scanning with ultrasound, although avoiding radiation exposure, is less apt to find small tumors. The combined use of ultrasound, mammography, and breast MRI is effective in saving the lives of women without a prior history of breast cancer, but is still not without risk of unnecessary and invasive biopsies in benign cases (Gotzsche and Nielsen, 2006). Serum biomarker tests such as PSA used in prostate cancer screening can similarly find early stage disease, but also increase the risk of unnecessary biopsies (Harris and Lohr, 2002). Other tumor marker tests such as CA-125, PSA, CEA, CA 19-9, and CA 15-3 have frequent false positives as they can be elevated in many non-cancerous inflammatory conditions; these too, if used in screening, would lead to many unnecessary biopsies. Thus, there remains a great need for new low cost, low-risk methods for primary cancer screening in the general population.

If indeed dogs are able to detect cancer in humans by sniffing biological samples such as exhaled breath or urine, then new avenues for earlier diagnosis of certain cancers could be possible. Interest in the potential analysis of volatile organic compounds for diagnostic purposes is growing and such a talent would be of great value in the development of diagnostic tests. We conducted this systematic review to ascertain whether dogs can detect human cancers with enough sensitivity and specificity to be useful for diagnostic purposes. Sensitivity is the proportion of cancer samples which the canines correctly identify, and specificity is the proportion of control samples which the canines correctly indicate as controls.

Section snippets

Study identification

We conducted a systematic search to identify all known published data on canine scent detection of cancers, following the “roadmap” suggested by Pai et al. (2004). We sought to find all published studies in which researchers trained dogs to detect human cancers using only their sense of smell, using biological samples such as skin, breath, urine, and excised tumor samples. Searches in PubMed (1949 to January 2009; www.pubmed.gov), and EMBASE (1980 to January 2009; http://embase.com), were

Results

We found 531 potentially relevant studies on the subject of canine detection of human cancers, and of these, excluded 520 and retained 11 (Figure 1). Full texts of the retained studies were examined. Five of these studies were excluded because they did not test canines detecting cancer, and 1 was excluded because it was a systematic review and did not include original data. A sixth unpublished manuscript was added to the 5 remaining articles to bring the total to 6 articles for review.

The study

Discussion

Five different teams of scientists have attempted to train dogs to detect and indicate lung, breast, melanoma, prostate, bladder, and/or ovarian cancer by smelling breath, urine, and tissue samples. Of 7 studies completed, 5 have met with statistically significant results and 4 have met with possibly clinically significant results. However, each of these studies could be improved to produce even better results. Training methods, sample storage method, target and control types used, and

Conclusion

Canine scent detection seems to be a valid method for cancer detection and may prove the principle that cancer can be detected by analysis of biological material such as urine or exhaled breath. Exhaled breath seems to be a better non-invasive biological sample than urine for biomarker analysis. Work done with malignant tissue samples was very accurate, but has no advantages over standard pathological examination of tumor tissue in that it still requires surgical removal. Work done with dogs

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