18F-rhPSMA-7.3 PET/MRI in Prostate Cancer Active Surveillance: a Pilot Study

Prostate cancer is the most common non-cutaneous malignancy in American men with the majority of men diagnosed with PSA-based screening. As such, many will be found to have low-risk disease when detected early in the disease course. Whole gland radical therapies with primary curative intent are typically invasive and incur a recognized risk of morbidity, particularly in regards to urinary and sexual quality of life measures. For this reason, patients with competing comorbidities or low risk disease have increasingly approached management with active surveillance. The use of active surveillance has increased significantly, particularly in those patients with low-volume, low-grade prostate cancer. For these surveillance protocols, serial PSA biomarker evaluation and periodic repeat prostate biopsies are scheduled to assess for grade or stage progression which may redirect management toward curative treatment options within the window for cure. Since the advent of prostate indication multi-parametric MRI (mpMRI) and its use to target areas of suspicion for biopsy sampling, MRI-TRUS fusion biopsy has been used in the setting of patients with active surveillance to better characterize disease risk stratification for confirmatory biopsy sampling. Despite the advances mpMRI has offered, its sensitivity for detection of clinically significant prostate cancer is insufficient to replace biopsy at both initial diagnosis and during active surveillance. Additionally, although MRI-TRUS fusion has improved detection of clinically significant cancers, it is known that a fraction of prostate cancers remain occult on mpMRI. Various PSMA radiotracers have been explored as an alternative to mpMRI for the detection of clinically significant prostate cancer. Many of these studies utilize PET/CT, which does not take advantage of the vast superiority of mpMRI over CT and limits their ability to detect clinically significant prostate cancer. However, early studies utilizing PET/MRI (in which the sensitivity of the exam for clinically significant cancer is improved by both the PET and MRI components) have shown promising results. While these studies have explored the role of PSMA-PET/MRI in lesion detection and biopsy guidance, there is little data regarding its use in the setting of active surveillance.