FDA Approves TLX591-CDx for Prostate Cancer Imaging

The FDA has approved the imaging product TLX591-CDx (Illuccix) as a radioactive diagnostic agent for PET of prostate-specific membrane antigen (PSMA) positive lesions in patients with prostate cancer who have suspected metastasis who are candidates for initial definitive therapy, and in those with suspected recurrence based on elevated serum prostate-specific antigen (PSA) level.¹

TLX591-Dx is described as a kit for the preparation of Gallium-68 gozetotide (PSMA-11) injection. The imaging product was investigated in 2 prospective, open-label trials: PSMA-PreRP (NCT02919111) and PSMA-BCR (NCT02918357), which demonstrated the efficacy of the imaging product as a detection method in prostate cancer.²

“The approval of Illuccix will give patients considerably improved access to PSMA-PET imaging, an advanced diagnostic tool that was recently included in the NCCN Clinical Practice Guidelines in Oncology for Prostate Cancer,” Oliver Sartor, MD, medical director at Tulane Cancer Center, said in a press release. “With patient doses able to be prepared on-site or via commercial radiopharmacy networks, either via generator or cyclotron, Illuccix delivers flexible patient scheduling and on-demand access throughout the day.”

In the two-center PSMA-PreRP trial, investigators enrolled 325 patients with biopsy-proven prostate cancer who were eligible for prostatectomy and pelvic lymph node dissection. All patients had to have either serum PSA of at least 10 ng/mL, a tumor stage cT2b or greater, or a Gleason score greater than 6. All patients were given the single gallium 68 PSMA-11 PET/CT or PET/MR from the mid-thigh to the skull base.

One hundred and twenty-three patients (38%) then proceeded to standard prostatectomy and template pelvic lymph node dissection and had sufficient histopathology data for evaluation. Of the evaluable patients, the mean age was 65 years (range, 45-76) and 89% were White. The median serum PSA was 11.8 ng/mL; the summed Gleason score was 7 (44%), 8 (20%), and 9 (31%). The remaining patients had Gleason scores of either 6 or 10.

Results showed that on patients who were PET-positive regardless of positive or negative histopathology, the positive predictive value was 61% (95% CI, 41%-81%). For those with PET-negative disease, the negative predictive value was 84% (95% CI, 79%-91%).

In the positive histopathology patients, the sensitivity rate was 47% (95% CI, 29%-65%), and in the negative histopathology subgroup, the specificity rate was 90% (95% CI, 84%-96%).

In the two-center, PSMA-BCR trial, investigators enrolled 635 patients had biochemical evidence of recurrent prostate cancer following definitive treatment with a serum PSA of more than 0.2 ng/mL more than 6 weeks after prostatectomy or by an increase in serum PSA of at least 2 ng/mL above nadir following definitive radiation. All patients received TLX591-Dx.

A total of 469 patients (74%) had at least 1 positive region that was detected by TLX591-Dx. The distribution of imaging was bone (34%), prostate bed (25%), pelvic lymph node (25%), and extrapelvic soft tissue (17%). There were 210 evaluable patients, of which the mean age was 70 years (range, 49-88), 82% were at least 65 years old, and 90% of patients were White. The median serum PSA was 3.6 ng/mL.

Prior therapy included radical prostatectomy (64%) and radiation (73%). Ninety-one percent (n = 192) were found to be true positive in at least 1 region against the composite reference standard (95% CI, 88%-95%). The proportion of patients who were true positive in 1 or more regions ranged from 82% to 97% among the pool of 9 readers used in the study. Additionally, the prostate bed had the lowest proportion of true positive results at the region-level (76% vs 96% for non-prostate regions).

As per the FDA approval, recommended amount of TLX591-Dx radioactivity for adults is 111 MBq to 259 MBq (3-7 mCi) as a bolus intravenous injection. Imaging should be conducted 50 minutes to 100 minutes following administration, and patients should void immediately prior to the start of imaging. Scans should begin caudally and proceed cranially.

Telix has a distribution network encompassing more than 140 nuclear pharmacies through its agreements with Cardinal Health and PharmaLogic; TLX591-Dx will be provided to more than 85% of eligible PET imaging sites in the United States.

“This heralds a new era of patient and physician access to gallium-based PSMA-PET imaging and marks an important new stage for Telix as we bring our first commercial product to market in the United States,” Christian Behrenbruch, MD, managing director and CEO at Telix, said in a press release. “Improved imaging can provide physicians with the insights to determine the most appropriate treatment pathway and give patients in the US access to a specific and sensitive imaging tool for the detection of prostate cancer throughout the body.”

References

1. FDA Approves Telix’s Prostate Cancer Imaging Product, Illuccix. News release. Telix Pharmaceuticals. December 20, 2021. Accessed December 20, 2021. https://bit.ly/3qaLqYv
2. TLX591-CDx (Illuccix). Prescribing information. Telix; 2021. Accessed December 20, 2021. https://bit.ly/3smma4n