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A nose for cancer


New research shows mice can detect differences between the urine of healthy mice and those with melanoma. Emma Culjat-Vukman reports

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Mice were successfully trained to discriminate between urine samples from mice with melanoma and from healthy mice

Mice can be trained to identify the odour of melanoma in urine before clinical signs appear, new research has suggested.

The finding, published in the Journal of Veterinary Behaviour, could lead to further work towards a non-invasive screening method for the early detection of this form of cancer.

For the study, researchers at the Institute of Genetics and Animal Biotechnology at the Polish Academy of Sciences collected urine from 40 male mice before and for four weeks after inoculating them with melanoma cells. Further groups of mice were then used in two behavioural experiments – one to test if mice showed any spontaneous preference for urine samples from healthy mice or from mice with melanoma, and one to see if mice could be trained to discriminate the odour of urine from mice with melanoma from that of urine from healthy mice.

Operant conditioning over the course of five months was used to train mice to distinguish the odour of urine from mice with melanoma. The mice were rewarded for identifying the right sample, and mildly punished (by a squirt of water) if they identified the wrong sample.

The mice in the first behavioural experiment showed no significant preference for urine samples from mice with melanoma or from healthy mice. In the second behavioural experiment, mice were successfully trained to discriminate between urine samples from mice with melanoma and from healthy mice. They could identify a sample from an affected mouse even if that individual was not showing visible signs of melanoma.

The researchers analysed urine from the mice inoculated with melanoma and from healthy mice to determine whether there were differences in their volatile organic compound (VOC) profiles – this could give a clue as to what the mice were detecting when differentiating between the two samples.

This analysis showed a pronounced decrease in two VOCs, n-hexane and methylene chloride, in mice with melanoma. The researchers suggest that this may be evidence that the odour of urine accompanying the development of melanoma is specific and differs from the odour of urine from healthy animals. They also suggest that the downregulation of some VOCs during tumour development may be related to the impact of tumour growth on the affected individual’s metabolism.

Animal olfactory detection of cancers has been well documented. Previous research has suggested that animals can help detect not just melanoma but also lung, bladder, breast, prostate and ovarian cancer, among others. Dogs are most frequently used for these studies, but nematodes and rats have also been investigated.

The researchers say that further work would be needed to determine if mice can detect other forms of cancer and also to investigate which particular VOCs are produced in the very early stages of various cancers. However, they hope that their work provides evidence to support continued research into the use of non-invasive early detection screening methods. If confirmed for other cancers, and for human odour donors, such simple screening methods could be applied to large human populations to identify suspect cases that require further diagnostic procedures to confirm or exclude malignancy. ●

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