Using parasites for pre-emptive cancer diagnosis

Roundworms and cancer are two words that are not often associated with each other, but in recent years there has been a discovery that has made this combination a topic of scientific interest. The parasites have been brought publicised in light of multiple infection reports including that of a 63-year-old Japanese male who was diagnosed with gastrointestinal cancer. After having experienced episodic gastric pain, roundworm larvae were found in his digestive system. The organisms had in fact attached themselves to a small ulcer in the man’s stomach that turned out to be in the early stages of gastrointestinal cancer. The roundworms were found to belong to the genus Anisakis: a group of parasitic nematodes which can be picked up by eating infected raw fish; a common component of the Japanese diet. The disease contracted from ingestion of the parasite is known as Gastrointestinal Anisakidosis, and is considered common in Japan. Although a rare occurrence, it was discovered that the attachment of Anisakis larva on to early tumours is not accidental.

Scientists Hirotsu, Sonoda and their colleagues conducted a series of experiments to determine whether or not the odour of cancerous lesions was what attracted the roundworms. They used Caenorhabditis elegans in their studies, a highly studied roundworm species. In one such experiment, they transferred droplets of cancer cell culture which had been grown, on to half of a petri dish. In the other half, they put droplets of non-cancer cell culture medium. When C. elegans were introduced into the dish, the worms moved towards the cancerous culture, suggesting an attraction. Other experiments in which the olfactory sensory neurons were removed from some of the roundworms showed that in the absence of the sense of smell, the worms often diverted away from the cancer cell culture and towards the fresh culture medium. This further suggested that the worms are attracted by scent.

False coloured image of C.elegans: the model organism used in the mentioned research. Image: Justin Chaplin (University of Queensland)

This finding has been a valuable one, as cancer is a worldwide leading cause of death. According to the world cancer report, figures are expected to continue to rise to an estimated 17 million deaths in 2030 alone. Cancer treatment technology has advanced significantly in recent years, however, there is still a need to develop effective and inexpensive methods of early diagnosis, as the condition often worsens and becomes increasingly difficult to treat as it progresses to the advanced stages.

Researchers realised the discovery could be used as a potential method of early cancer diagnosis, using human urine instead of cancer and non-cancer cell cultures. C. elegans were placed in the vicinity of the urine of cancer and non-cancer patients. The worms were attracted to the urine samples of cancer patients, successfully identifying all nine types of cancers they were exposed to 96% of the time. Three of the nine test cancers were colon, prostate and breast cancers. This mode of diagnosis is now called the Nematode Scent Detection Test (NSTD), and this finding will hopefully be used as a system of diagnosis given its affordability and non-invasive protocol.

Previous literature has shown that using animals to detect cancer in humans is not a novel concept; dogs and mice have been used successfully for such diagnoses, however, training complex organisms to detect the scent for clinical application is impractical as the accuracy is dependent upon the animal’s ability to concentrate on the task. Introducing simple organisms such as the C.elegans for cancer diagnosis proves to be a more accurate, accessible and inexpensive method.

Further investigation into the method is being conducted, and hopefully, within the foreseeable future, patients could send urine samples from the comfort of their own homes and receive fast and accurate diagnoses. This early detection method could prove of vital importance for the successful eradication of cancer. Its low cost, convenience and speed will hopefully help decrease the number of cancer-related fatalities worldwide. It is one of many tools capable of making eradication a reality.