Patient-specific targeted analysis of circulating tumour DNA in plasma is feasible and may be a potential biomarker in UTUC

Purpose The prognosis of upper urinary tract urothelial carcinoma (UTUC) is associated with tumour grade (G) and stage.

Despite preoperative risk stratification and radical treatment, recurrence and progression are common.

Thus, prognostic and monitoring biomarkers are needed.

This feasibility study aimed to investigate if targeted analyses on circulating tumour DNA (ctDNA) in plasma could identify tumour-specific gene variants, and thus have potential for further evaluation as a biomarker in UTUC.

Methods Nine UTUC patients with genetically characterised tumours were included in this prospective pilot study.

Two tumour-specific variants were chosen for targeted analyses with multiplex droplet digital PCR on cell-free DNA (cfDNA) from plasma at diagnosis or from recurrence.

Results Of six patients with diagnostic plasma samples, ctDNA was detected in four with G2 or G3 tumours and tumours > 300m^2 in size.

Three of these patients progressed in their disease and the fourth had the largest G3 tumour at sampling.

In contrast, the two patients with undetectable ctDNA in diagnostic plasma had a G1 tumour and G3 carcinoma in situ (CIS), respectively.

The patient with G3 CIS had detectable ctDNA later during follow-up and progressed thereafter with aggressive intravesical recurrence and CT-scan-verified CIS progression in the upper urinary tract.

In three patients with small recurrent G1 or G2 tumours, none had detectable ctDNA in plasma and all were progression free.

Conclusion Our early findings demonstrate that ctDNA in plasma can be detected by targeted analysis in patients with UTUC.

However, further studies are needed to determine its role as a potential biomarker.