PSMA PET/CT for Biochemical Recurrence Detection in Patients With Prostate Cancer

In France, prostate cancer is the most common cancer in men over 50 years of age (nearly 50,000 new cases per year) and is the third leading cause of cancer-related death in men (approximately 9,000 deaths per year).

Among patients who have undergone a curative treatment strategy for localized prostate cancer, between 27% and 53% of them will have a biochemical recurrence within 10 years.

Biochemical recurrence is defined as :

• After total prostatectomy by the persistence of a detectable PSA or the reappearance of a detectable PSA above 0.2 ng/ml after a more or less long period of undetectability.
• After conservative treatment (radiotherapy or brachytherapy) by an increase in PSA above a threshold set at nadir +2 ng/ml Biological recurrence precedes the occurrence of symptomatic metastases by an average of 7-8 years.

Currently, after prostatectomy, when the PSA is < 1 ng/mL, no imaging test is recommended for the assessment of recurrence (grade A recommendation).

The sensitivity of currently available tests does not provide sufficiently discriminating information for this PSA value.

Multiparametric MRI performs well in detecting local recurrence, particularly in the case of PSA > 1 ng/mL (sensitivity of 98%, specificity of 94% for the detection of 5 mm lesions).

18F-choline positron emission tomography (PET-choline) is of interest in the detection of distant lymph node and/or visceral recurrences; indeed, PET-choline has proven its superiority in detection compared with conventional examinations, particularly for PSA values above 2ng/ml with a detection rate of up to 90%.

However, the performance of this examination remains dependent on the PSA level and is low when the PSA level is below 1 ng/ml (sensitivity around 5-24% for a PSA below 1 ng/ml).

The performance of PET-choline is optimised for low PSA by taking into account the PSA doubling time and velocity.

Recently, prostate specific membrane antigen ligand positron emission tomography (PET-PSMA) has emerged as the most promising new molecular imaging modality for the management of prostate cancer.

Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein selectively overexpressed in 90-100% of prostate cancer lesions, as well as in metastatic lymph nodes and bone metastases, making it an ideal target for molecular imaging of prostate cancer.

This tracer appears to perform better than other imaging modalities, particularly for low PSA values, with a detection rate of 50% for a PSA level below 0.5 ng/ml compared to 5-20% with PET-choline. Indeed, a 2019 meta-analysis evaluating the value of PSMA-PET in patients with biologic recurrence of prostate adenocarcinoma reported detection rates of 45%, 59%, 75% and 95% for PSA levels < 0.5 ng/mL, between 0.5 and 0.9 ng/mL, between 1 and 1.9 ng/mL and 2 ng/mL respectively.

The aim of this study is to evaluate PSMA ligand PET for the detection of occult biological recurrence in patients with prostatic neoplasia referred to the Brest University Hospital .