COMBINING MRI with prostate-specific membrane antigen (PSMA) PET has been found to improve the detection of clinically significant prostate cancer in an MRI triaged population and can potentially allow a reduction in the number of prostate biopsies required for diagnosis.
The researchers conducted a prospective, multi-centre Phase II imaging trial across three institutions in Australia. Men were eligible if they were suspected of having prostate cancer based on prostate-specific antigen levels less than 20 ng/mL or an abnormal digital rectal examination. In total, 291 men underwent MRI, PSMA-based PET imaging, and biopsy. Of these individuals, 56% had clinically significant prostate cancer, 67% had a positive MRI, 73% had a positive PSMA PET, and 81% had a positive combined MRI plus PSMA PET. Combined MRI and PSMA improved the negative predictive value relative to MRI alone (91% and 72%, respectively), a difference that was found to be statistically significant (p<0.001). In addition, sensitivity was significantly improved for the combined approach compared with MRI alone (97% versus 83%, respectively). Despite this, specificity was 40% with the combination but 53% with MRI alone (p=0.011). Moreover, positive predictive value was similar (67% for MRI combined with PSMA PET and 65% for MRI alone; p=0.4).
Five clinically significant prostate cancer cases were missed with the combination of PSMA PET and MRI: four Internaional Society of Urological Pathology (ISUP) Grade 2 and one ISUP Grade 3.
Although not involved in the research, Thomas Hope, Director of Molecular Therapy in the Department of Radiology and Biomedical Imaging at the University of California San Francisco (UCSF), California, USA, shared his perspective on the study: “It remains unclear, even in light of this study, what role PSMA PET will have in patients on active surveillance and undergoing biopsy, but the results provide insight into the potential benefit of adding PSMA PET to MRI in order to better select patients for biopsy.”
The authors concluded: “Given the high sensitivity of PSMA+MRI in detection of clinically significant prostate cancer and the predominately low-grade characteristics of the cancers missed, it appears acceptable to avoid biopsy in men with negative PSMA+MRI findings, in the absence of subsequent concerning PSA [prostate-specific antigen] kinetics.”