Detection of a bowel cancer marker (CDH1) in wastewater may offer a new community level early warning system for the disease, suggests a proof of concept study published online in the Journal of Epidemiology & Community Health.
Wastewater surveillance could complement traditional screening methods and could help target areas for cost-effective, practical community screening, particularly amid rising rates of the disease among young people, say the researchers.
In the USA alone, there are an estimated 154,000+ new cases of bowel cancer every year, making this the third most common cancer and the second leading cause of cancer-related deaths in the country, as the disease is often diagnosed at a late stage, highlight the researchers.
Wastewater in sewers can be used to monitor a wide range of biological compounds shed in urine and faeces, but it's not known if such an approach might work for community surveillance of bowel cancer, explain the researchers.
To find out, they reviewed the details of patients treated with bowel cancer at a tertiary care centre in Jefferson County, Kentucky, between 2021 and 2023, to identify geographical clusters of high incidence rates of the disease.
Clusters were defined as areas with more than 4 bowel cancer cases within a half-mile radius. Next, sex-and age-standardised rates of bowel cancer were calculated from state cancer registry data for diagnoses captured between 1995 and 2018.
Three geographical areas of high bowel cancer incidence and one area where none of the tertiary care or state cancer registry patients lived, were selected for neighbourhood wastewater analysis.
Wastewater samples (175 ml) were collected three times from each of four sewersheds at 7:00, 10:00, and 13:00 hours over the course of one day (26 July 2023).
The researchers analysed the samples for human RNA biomarkers: CDH1, which is associated with cancer; and a general cell maintenance marker GAPDH (glyceraldehyde 3-phosphate dehydrogenase) to use as a control.
All the samples from all four clusters showed detectable levels of these compounds. Average levels of CDH1/GAPDH markers for the three clusters were 20 (cluster 1), 2.2 (cluster 2), and 4 (cluster 3), compared with 2.6 in the comparison cluster.
Cluster 1 had more than double the number of known tertiary care centre patients per 100 people when compared with the other two clusters, which might explain the wide variation in the figures, say the researchers. Some residents in the control cluster may also have been treated for cancer elsewhere.
This is a proof of concept study, and further research will be needed, they caution, acknowledging various limitations to the findings. It's not clear how the CDH1:GAPDH ratio in wastewater specifically relates to new cases of bowel cancer, and whether this represents diagnosed or undiagnosed cases, for example.
The small sample size and geographical scope limit the wider applicability of the findings, while the sensitivity and specificity of wastewater-based epidemiology for detecting bowel cancer biomarkers require validation in larger groups of people, they point out.
But they emphasise: "The recent trend of increasing [colorectal cancer] incidence in younger populations underscores the need for improved public health approaches. While existing screening methods like colonoscopy and stool-based tests remain effective, their reliance on individual compliance presents challenges, particularly in communities facing structural and social determinants of health barriers."
And they suggest: "Detecting elevated [colorectal cancer] markers across broader community zones, before high incidence is recorded by tertiary care centres or state cancer registries, could help target areas for practical, cost-effective, community screening.
"This approach may enable early diagnosis while also identifying regions with a lower likelihood of case discovery, enabling timely clinician alerts."
