Targeted biopsies are redundant in mp-MRI and PSMA- PET proven radiorecurrent prostate cancer

Abstract

Purpose or Objective Radiorecurrent prostate cancer is conventionally confirmed using systematic and/or targeted biopsies. The availability of multiparametric (mp) MRI and more recently prostate specific membrane antigen (PSMA) PET-CT has increased diagnostic accuracy in the radiorecurrent setting. It is unknown whether pathology verification remains necessary with these imaging modalities combined. Especially in the radiorecurrent setting where they might have higher diagnostic accuracy compared to diagnosis of primary prostate cancer due to fibrotic and inactive surrounding prostate tissue. Materials and Methods Patients treated with MRI guided focal salvage high dose rate (HDR) brachytherapy from July 2015 to January 2018 were included in the current analysis. Patients were part of a prospective cohort and phase II study (PRECISE; https://www.trialregister.nl/trial/6827) investigating a single 19 Gy dose to the recurrent tumour after primary radiotherapy. Patients were staged with 3T mp-MRI (recurrence suspicion on T2, dynamic contrast enhanced and/or diffusion weighted imaging) and PSMA PET-CT. Both imaging modalities were fused and used to delineate the gross tumor volume (GTV) on MRI. The GTV was transperineally biopsied using transrectal ultrasound fused with MRI. Treatment was performed using MRI-guidance of catheter positions. Results A total of 42 patients were identified from the database who had both mp-MRI and PSMA PET-CT positive recurrence in the prostate and underwent cognitive (n=7) targeted or MRI-TRUS fusion targeted (n=34) biopsies (n=1 unknown). A total of 37 (88%) patients had positive biopsies for cancer. Four patients were initially negative (all MRI-TRUS fusion targeted) and were re-biopsied after which recurrent prostate cancer was verified. Only one (2.4%) patient had negative biopsies and refused re-biopsy. We observed higher PSMA standardised uptake values (SUV) in patients with Gleason sum score 7-9 compared to 6: median 9.3 versus 4.9 (p=0.02). An example of the adopted imaging modalities is shown in figure 1. Conclusion In patients with radiorecurrent prostate cancer, with a concordant lesion on mp-MRI and PSMA PET-CT, targeted biopsies have a minimal detection rate of 97.6%. Biopsies can therefore safely be withheld in these patients, thereby avoiding an unnecessary invasive and burdensome procedure. Higher PSMA SUV values might lead to higher detection rates.