Olfactory Detection of Prostate Cancer by Dogs Sniffing Urine: A Step Forward in Early Diagnosis

Abstract

Background

Volatiles organic compounds (VOCs) in urine have been proposed as cancer biomarkers.

Objective

To evaluate the efficacy of prostate cancer (PCa) detection by trained dogs on human urine samples.

Design, setting, and participants

A Belgian Malinois shepherd was trained by the clicker training method (operant conditioning) to scent and recognize urine of people having PCa. All urine samples were frozen for preservation and heated to the same temperature for all tests. After a learning phase and a training period of 24 mo, the dog’s ability to discriminate PCa and control urine was tested in a double-blind procedure. Urine was obtained from 66 patients referred to a urologist for elevated prostate-specific antigen or abnormal digital rectal examination. All patients underwent prostate biopsy and two groups were considered: 33 patients with cancer and 33 controls presenting negative biopsies.

Measurements

During each “run,” the dog was asked to signal a cancer urine among six samples containing only one cancer urine and five randomly selected controls. Sensitivity and specificity of the test were assessed.

Results and limitations

The dog completed all the runs and correctly designated the cancer samples in 30 of 33 cases. Of the three cases wrongly classified as cancer, one patient was rebiopsied and a PCa was diagnosed. The sensitivity and specificity were both 91%.

Conclusions

This study shows that dogs can be trained to detect PCa by smelling urine with a significant success rate. It suggests that PCa gives an odor signature to urine. Identification of the VOCs involved could lead to a potentially useful screening tool for PCa.

Introduction

Prostate cancer (PCa) is the most frequent noncutaneous malignancy in men, with an incidence as high as 192 280 cases per year in the United States [1]. Although prostate-specific antigen (PSA) blood testing remains the most widely used tool for PCa detection [2], important efforts have been conducted to determine alternative biomarkers to overcome its lack of specificity [3]. Novel urine or blood biomarkers have been proposed in the last decade, but none of them is currently widely used [4].

Volatile organic compounds (VOCs) in urine have been proposed as alternative biomarkers [5]. In the case of PCa, it can be postulated that specific VOCs may be present in urine that reveal the presence of a malignant tumor. Basic research has provided a recent finding suggesting that sarcosine could be an indicator of the aggressiveness of prostatic malignant disease [6], but no extensive work searching for VOCs in urine related to the presence of PCa has been published. Promising results about other malignant diseases have been presented [7].

VOC detection can be made by sophisticated biochemical techniques or using animals that have a highly sensitive sense of smell [7]. Some previous work suggested that dogs trained to smell urine could recognize lung, bladder, or breast cancer with various success rates, but no positive results have been published concerning PCa [8], [9]. To determine if some VOCs in urine could result in a specific odor associated with PCa, we specially trained a dog and conducted a double-blind study to check its ability to detect PCa by sniffing urine.