18F-rhPSMA-7.3 Performance for Detecting PLN Metastases

By Patrick Daly - Last Updated: December 2, 2022

In the phase 3 LIGHTHOUSE study, researchers established the first data, to their knowledge, on the diagnostic performance and safety of prostate-specific membrane antigen (PSMA) positron emission tomography (PET) for prostate cancer imaging with the PSMA ligand ¹⁸F-rhPSMA-7.3. Findings were presented by study lead, Brian F. Chapin, at the 23rd Annual Meeting of the Society of Urologic Oncology.

The researchers concluded that ¹⁸F-rhPSMA-7.3-PET/computed tomography (CT) provided clinically useful information for detecting N1 stage disease, particularly in high-risk or very high-risk patients. They did note that the lower sensitivity observed in the study was consistent with published evidence on PSMA-targeted diagnostic radiopharmaceuticals and was balanced by high specificity.

¹⁸F-rhPSMA-7.3-PET/CT Shows Low Sensitivity but High Specificity

The efficacy analysis population (EAP) included 296 patients, of which 121 (41%) had T1 stage disease, 112 (38%) had T2, and 45 (15%) had T3. The population’s last median prostate-specific antigen was 8.45 (range, 1.15-120), and 197 (67%) patients were considered to have high-risk or very high-risk disease.

The primary end point was patient-level sensitivity and specificity of ¹⁸F-rhPSMA-7.3-PET for identifying pelvic lymph node (PLN) metastases in patients scheduled to undergo radical prostatectomy (RP), as independently evaluated by 3 blinded central readers.

According to the report, the 3 readers reported 23-37 (7.7%-13%) patients in the EAP had ¹⁸F-rhPSMA-7.3-positive PLN metastases. The 3 readers calculated that ¹⁸F-rhPSMA-7.3-PET/CT had a sensitivity for PLN metastases detection of 30% (95% CI, 19.6-42.1), 27% (95% CI, 17.2-39.1), and 23% (95% CI, 13.7-34.4), respectively, which were below the prespecified threshold for significance.

Comparatively, the readers calculated that ¹⁸F-rhPSMA-7.3-PET/CT had a specificity of 93% (95% CI, 88.8-95.9), 94% (95% CI, 89.8-96.6), and 97% (95% CI, 93.7-98.7), respectively, which were all above the threshold for significance. The authors noted no serious adverse events were reported.

“In summary,” the report concluded, “¹⁸F-rhPSMA-7.3 is well-tolerated by patients and exhibits a favorable benefit-to-risk ratio in men with newly diagnosed prostate cancer scheduled for RP and PLN dissection.”