The detection of prostate cancer using the odour of patients' urine is the subject of two new studies, and on the basis of this evidence, our furry friends could now have a serious electronic contender. An attempt to train 10 dogs to discriminate urine of men with prostate cancer from cancer-free controls was unable to show a better-than-chance ability in any dog, whereas a handheld electronic device, or eNose, was used to assign urine samples to prostate cancer and BPH groups with sensitivity and specificity comparable to the PSA assay.

Credit: MACMILLAN AUSTRALIA

The remarkable olfactory powers of dogs have been under investigation for some years, with mixed results in the detection of different cancers. Elliker et al. sought to validate a training protocol that used large numbers of urine samples (50 prostate cancer and 67 controls) in the hope of developing generalized prostate cancer recognition. Based on their performance, only two of the 10 dogs were selected to proceed from training to the testing stage, but the sensitivity (0.13 and 0.25 for the two dogs) and specificity (0.71 and 0.75) of prostate cancer sample detection in double-blind tests involving different samples to those used in training was disappointing. Elliker et al. suggest that dogs can memorize the odours of many more training samples than previously believed, and that the challenge is now to teach the animals to respond to a common odour indicative of cancer.

In a parallel approach, Roine et al. used an eNose device, developed for detection of chemical warfare agents and toxic industrial compounds, to produce 'smell prints' from the urine headspace of samples from 50 men with prostate cancer and 15 with BPH. Smell prints consisted of measurements from 16 channels of an ion mobility cell, and linear discriminant analysis was used to assign the print from each sample into prostate cancer or BPH classes. With statistical analysis to avoid overly positive results, sensitivity and specificity were 78% and 67%, respectively. Results were not affected by prostate volume.

For dogs, the pros of a highly developed intrinsic olfactory sense and ability to respond to training are balanced by heterogeneous responses and our incomplete understanding of the mechanism of scent learning. The eNose offers the prospect of noninvasive, standardized detection of prostate cancer in any setting. Further studies are required to optimize the detection protocol and to determine whether the eNose is also capable of providing a measure of cancer aggressiveness.