Patients with an intraprostatic recurrence after radiotherapy can be considered for salvage therapy. The EAU guidelines recommend obtaining histological confirmation before salvage therapy. This recommendation, however, does not consider the diagnostic accuracy of PSMA PET/CT. In current daily clinical practice, the need to obtain histological confirmation is often deemed unnecessary as a result of the recognized high specificity of PSMA PET/CT, which nowadays is the modality of choice for detecting recurrences. In this study, we evaluated the biopsy outcomes in patients with an intraprostatic recurrence on PSMA PET/CT after prostate whole gland radiotherapy.
We retrospectively included 51 consecutive patients who were detected with solely an intraprostatic recurrence post-radiotherapy on PSMA PET/CT in the Netherland Cancer Institute and Erasmus MC and underwent prostate biopsies. Whole prostate radiotherapy (n=39 external beam radiotherapy and n=12 brachytherapy) was the initial curative therapy in all patients. A prostate mpMRI was performed next to PSMA PET/CT in 44 patients. Information on repeat biopsy and PSMA PET/CT was collected. True positivity of PSMA PET/CT was defined as biopsy confirmed recurrence (first or repeat biopsy) or if there was radiological progression of the intraprostatic lesion on subsequent imaging.
The median PSA at the time of PSMA PET/CT was 3.7 (interquartile range (IQR) 2.5-5.6) ng/ml. The median time between initial radiotherapy and PSMA PET/CT was 75 (IQR 52-97) months. The initial prostate biopsy confirmed the intraprostatic recurrence in 36 (71%) patients. Additionally, 6 out of 8 patients who underwent repeat biopsies were diagnosed with an intraprostatic recurrence and 3 of 6 patients with subsequent imaging showed progression. Positive predictive value (PPV) of PSMA PET/CT was 88.2%. Only 4 patients had a negative MRI (PIRADS≤2) of which 3 had a negative prostate biopsy and no progression on subsequent imaging. The PPV for patients with a positive MRI (PIRADS≥3) and PSMA PET/CT was 92.5% (total 40 patients, 34 histological confirmed, 3 with radiological progression). Incorrect prostate sampling delayed the initiation of salvage therapy in 9 patients with a median of 9 (IQR 5-13) months.
A considerable part of patients with an intraprostatic recurrence on PSMA PET/CT post-radiotherapy will have a negative (initial) prostate biopsy. Of these patients, however, most will have positive repeat prostate biopsy or radiological progression on repeat imaging. The high PPV of combined PSMA PET/CT and MRI positivity justifies the initiation of salvage focal therapy without histological confirmation to prevent unnecessary delay. In patients without evidence of an intraprostatic recurrence on MRI histological confirmation is necessary before initiation of salvage therapies.