Telix Pharmaceuticals has released new data showing that its positron emission tomography (PET) imaging agent, Zircaix (TLX250-CDx), helps in planning better clinical management for nearly half of patients with indeterminate renal masses (IRMs).

New data from the ZIRCON-X study indicate this imaging diagnostic tool could help reduce unnecessary invasive procedures and optimize treatment pathways. ZIRCON-X was a non-interventional, prospective, post-hoc study assessing imaging data collected during Telix’s parent pivotal Phase III ZIRCON trial (NCT03849118).

Study Details and Clinical Impact

The ZIRCON-X analysis assessed the impact of adding Zircaix PET/CT to the standard diagnostic workup for 294 patients with IRMs—small kidney masses where the cancer type is unclear from conventional imaging, like a CT (computed tomography) scan or an MRI (magnetic resonance imaging).

Multi-disciplinary teams (MDTs) from four institutions first proposed a management plan based on standard-of-care imaging. After a minimum four-week interval, the same MDTs re-evaluated the cases with the additional information from the Zircaix scan.

The results, to be presented at the 2025 Society of Urologic Oncology Annual Meeting, were striking: about half (48.6%) of patients would have had a change in their clinical management based on the new PET imaging data.

A Shift Toward Precision Management

Beyond the overall change, the analysis revealed substantial shifts in patient care strategies. More than one-third of patients (37.4%) experienced a ‘major change’ in their management plan. These significant alterations included:

• Treatment Escalation or De-escalation: Approximately 30% of all evaluable patients had their treatment plans intensified or reduced in aggressiveness. For instance, 18 patients initially selected for active surveillance would have been escalated to immediate treatment.
• Avoiding Invasive Procedures: Over 20% of the patients whose management changed (31 patients) could have potentially avoided an invasive biopsy.
• Surgical Refinement: In cases where surgery remained the chosen path, Zircaix provided superior clarity on the spatial localization of clear cell renal cell carcinoma (ccRCC) within the kidney. This allowed physicians to better determine the most appropriate procedure, such as opting for kidney-sparing partial nephrectomy over total removal.

Mechanism and Diagnostic Performance

Zircaix is an investigational diagnostic radiopharmaceutical that targets carbonic anhydrase IX (CAIX), a cell surface protein highly expressed on over 95% of ccRCC cells but generally absent in healthy kidney tissue. By binding to this target, the agent produces high-contrast PET/CT images that help characterize the molecular phenotype of a renal mass.

This builds on the data from the ZIRCON trial, which demonstrated the agent’s high diagnostic accuracy, with 86% sensitivity and 87% specificity for detecting ccRCC.

Professor Karolien Goffin, a principal investigator on the studies, noted that the results “demonstrate that TLX250-CDx PET/CT has significant potential to impact clinical decision making… and give physicians greater confidence in clinical planning.”

Dr. David N. Cade, Telix’s Group Chief Medical Officer, emphasized that the agent addresses an “unmet need for better non-invasive diagnostic work-up for ccRCC that can improve risk stratification and minimize overtreatment and undertreatment.” Adding that the agent has recently been included in international renal imaging guidelines.

The data from the ZIRCON-X analysis are expected to help in Telix’s forthcoming application for marketing authorization of Zircaix in Europe.