Florence Le Calvez-Kelm, Scientist and Principal Investigator, Genomic Epidemiology Branch, International Agency for Research on Cancer, World Health Organization, unpacked recent developments regarding the application of digital droplet PCR in urine to detect and monitor bladder cancer. She argued that this method is cost-effective and easy to implement in the clinic.
Bladder cancer is the 10th most common cancer in the world and has one of the highest rates of recurrence. The risk factors include tobacco smoking (attributed to almost 50% of cases) and exposure to chemicals at work estimated at 3-5% by IARC, but higher in recent reports from France.
The principal symptom of bladder cancer is the detection of blood in urine. There are some FDA-approved biomarkers, but biomarkers are not typically used in routine practice due to performance consistency issues, and others are still being developed and commercialised. The main diagnostic procedure for bladder cancer is cystoscopy which is expensive and invasive so there is a demand for non-invasive methods like urine cytology.
TERT promoter mutations have been found in over 80% of bladder cancer and in carcinomas of the upper urinary tract systems and in 2014 a French group reported that it is possible to detect TERT promoter mutations in urine.
Le Calvez-Kelm used NGS and digital droplet PCR to target cell-free DNA in the urine and detected two key mutations, C228T and C250T which are highly prevalent in bladder cancer. In collaboration with a local hospital in Lyon, Le Calvez-Kelm collected urine samples from bladder cancer patients. Using NGS, TERT mutations were detected in 87% of cancer cases with 95% specificity. Furthermore, there was a high concordance (98%) between cfDNA and urine pellet DNA. Another crucial finding from the study was that TERT mutations were detectable across all risk categories and outperformed urine cytology in detecting low-grade tumours. The team later transitioned to ddPCR for its speed, cost-effectiveness, and clinical feasibility.
Le Calvez-Kelm also conducted a follow-up study, monitoring the cancer recurrence in this French cohort called the DIAGURO cohort. The analysis showed that mutation levels dropped post-treatment but rose again before clinical confirmation of recurrence. Le Calvez-Kelm explained that they encountered technical challenges, such as the GC-rich nature of the TERT region which complicates PCR. Luckily, they were able to overcome this by using deaza-dGTP to linearise the DNA.
Overall, these findings back ddPCR as a sensitive, simple, and scalable method for bladder cancer detection and monitoring. The team aims to translate these results into clinical practice and policy through targeted communication with stakeholders.
