Radiohybrid PSMA PET imaging has favourable detection rate for prostate cancer recurrence

The ability to determine the extent and location of recurrent prostate cancer is key for physicians and their patients. Conventional imaging techniques have many limitations in prostate cancer identification and localisation. In the SPOTLIGHT study, ¹⁸F-rhPSMA-7.3 PET imaging proved to have a favourable detection rate for prostate cancer recurrence.

Up to 40% of patients who undergo radical prostatectomy and up to 50% of patients who undergo radiation therapy will develop local or distant recurrences within 10 years [1]. The ability to determine the extent and location of recurrent prostate cancer is key for appropriate clinical management. However, conventional imaging techniques have many limitations in prostate cancer identification and localisation, and greater imaging accuracy is needed throughout the care continuum to optimise therapeutic decision‐making.

The SPOTLIGHT study (NCT04186845) aimed to evaluate ¹⁸F‐rhPSMA‐7.3 PET imaging as a potential decision‐making aid by determining suspected biochemical recurrence of prostate cancer across a wide PSA range. Enrolled were 389 men with a history of localised prostate cancer with prior curative-intent treatment, an elevated PSA suspicious of biochemical recurrence (median PSA 1.10 ng/mL), and who were potentially eligible for salvage therapy with curative intent. All patients underwent PET for 50–70 minutes after IV administration of 296 MBq ¹⁸F-rhPSMA-7.3 [2]. Coprimary endpoints were the Correct Detection Rate (CDR; i.e. percentage of patients scanned with ≥1 true positive lesion) and Positive Predictive Value (PPV; i.e. all PET-positive regions combined) of ¹⁸F-rhPSMA-7.3 using histopathology and/or conventional imaging as a composite standard of truth (SoT). These metrics were also evaluated in a subset of patients with a histopathology-only SoT. Prespecified statistical thresholds of at least 36.5% and 62.5% were set for CDR and PPV, respectively. Overall detection rate stratified by PSA was also documented. Dr David Schuster (Emory University School of Medicine, GA, USA) presented the results [1].

In 389 men who had an evaluable ¹⁸F-rhPSMA-7.3 scan, the overall detection rate was 83% by majority read (see Figure). In 366 men with a composite SoT, the CDR was 56.8%, meeting the prespecified threshold. The PPV was 59.7%, not meeting the prespecified threshold. In the subset of patients with a histopathology-only SoT, the CDR and PPV were higher at 81.2% and 71.6%, respectively. Both of these values met the prespecified thresholds.

Figure: Overall detection rate with ¹⁸F-rhPSMA-7.3 PET [1]



There were no serious adverse events related to ¹⁸F-rhPSMA-7.3. The most frequently reported adverse events were hypertension (1.8%), diarrhoea (1.0%), injection site reaction (0.5%), and headache (0.5%).

Based on these results, Dr Schuster concluded that ¹⁸F-rhPSMA-7.3 has a clinically meaningful CDR that meets the prespecified threshold. Overall detection rates are high even at low PSA values. Together, these results support the clinical utility of ¹⁸F-rhPSMA-7.3 PET in men with recurrent prostate cancer across a wide PSA range.

1. Schuster DM, et al. Detection Rate of 18F-rhPSMA-7.3 PET in Patients with Suspected Prostate Cancer Recurrence: Results from a Phase 3, Prospective, Multicenter Study (SPOTLIGHT). Abstract 9, ASCO GU 2022, 17–19 February.
2. Eiber M, et al. J Nucl Med. 2020;61:696-701.

 

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Posted on 8 April, 20228 April, 2022