Stage migration in prostate cancer: the role of PSMA-PET in identifying oligometastatic disease

Oligometastatic disease (OMD) represents an intermediate disease state between localized and metastatic prostate cancer (PCa), where patients may still benefit from curative treatments. The prevalence of "de novo" metastatic disease detected by positron emission tomography (PET) with prostate specific membrane antigen (PSMA) in a real-world setting is still to be clarified. The primary aim was to compare the detection rates of OMD between PSMA-PET and conventional imaging (CI) in patients with intermediate- to high-risk PCa.

This multicenter retrospective study included patients with intermediate- to high-risk PCa who underwent both PSMA-PET and CI (contrast-enhanced CT and bone scintigraphy) within four months. The primary endpoint was to compare the detection rates of OMD (defined as ≤ 3 metastatic) between PSMA-PET and CI. The secondary endpoint was to assess treatment changes prompted by PSMA-PET findings.

Data of 497 patients were collected, and 255 patients met inclusion/exclusion criteria for the primary endpoint analysis, and all were considered for the secondary endpoint. OMD was identified using PSMA-PET in 11.4% of patients (29/255), significantly higher than the 6.7% rate (17/255) with CI (p = 0.040). In a retrospective multidisciplinary review, the intended clinical management changed in 36.5% (93/255) of cases, with major changes in 18.5% (e.g. a switch from curative therapy to systemic treatment) and minor changes in 18.0%. This reflects the intended treatment plan, not the treatment delivered. Limitations include the retrospective design, lack of central imaging review and absent patient follow-up. Also, the impact of PSMA-PET on survival has not been established.

This study shows that CI may underestimate de novo metastatic prostate cancer. Compared with CI, PSMA-PET detected more patients with de novo oligometastatic and multimetastatic disease and produced stage migration in intermediate- to high-risk patients. These findings reflect increased detection and reclassification, and were associated with changes in the intended treatment plan. However, because no independent reference standard or follow-up was available, they do not establish improved diagnostic accuracy.