Active surveillance is an established standard of care for patients with low-risk prostate cancer. Conversely, “intermediate” risk prostate cancer is a heterogenous disease state, for which active surveillance may be an appropriate management strategy for a subset of such patients. Given the increased popularity of active surveillance for this cohort of patients, imaging-based tools for their stratification have emerged.
The PRIMARY trial was a prospective multicenter phase II imaging trial that enrolled men with suspected prostate cancer (PCa), no prior biopsy, and a recent mpMRI examination within 6 months, and for whom prostate biopsy was planned. In total, 291 men underwent an mpMRI, 68Ga-PSMA PET/CT, and systematic biopsy with or without targeted biopsy.
A combined mpRMI + PSMA-PET/CT approach improved the sensitivity from 83% with MRI alone to 97% when combined (NPV: 72% to 91%), at the expense of decreased specificity (53% reduced to 40%). Significantly, a combination approach reduced the false negative rate for detection of clinically significant prostate cancer (csPCa) from 17% to 3.1%.1
Interestingly, there was a direct correlation between the SUVmax level and increased/worsening ISUP grade group disease. The probability of csPCa increased exponentially as the SUVmax increased from 2.5 to 10, with the probability of csPCa leveling off at 1.0 for lesions/patients with SUVmax of 10 or greater.
Among patients with an MRI positive lesion (PIRADS 4/5) and a PSMA positive scan with an SUVmax of >9, the PPV for csPCa was 100%. A similar PPV of 100% for csPCa was observed when patients had any MRI (PIRADS 2/3) and a PSMA positive scan with an SUVmax of >12.
Can we combine the SUVmax score with other PET-generated parameters to produce a scoring system that predicts the likelihood of csPCa? The PRIMARY score was derived based on the intensity and pattern of uptake with a 5-point Likert scale analogous to that of the PIRADS for mpMRI.2
Similar to the PIRADSv2 scoring system, patients with PRIMARY score lesions of 3 or worse are generally considered to have “positive” lesions:
- SCORE 3: Focal transition zone uptake
- SCORE 4: Focal peripheral zone uptake
- SCORE 5L SUVmax >12
Dr. Eapen next highlighted a case study of a patient with GG2 disease and 2 lesions with PRIMARY scores of 1 and 2, respectively.
She contrasted that with a second scenario of a similar patient with GG2 disease, but now with 2 lesions of PRIMARY scores 4 and 5, respectively. In her practice, the first patients would be a suitable candidate for active surveillance given that his risk of high-grade disease is considerably low if re-biopsied. Conversely, given the location/intensity of tracer uptake in the 2nd patent’s PSMA-PET/CT, there would be considerable concern for underlying high-grade disease, and this patient would thus be likely offered radical treatment.
Presented by: Renu Eapen, MBBS, FRACS (Urol), Department of Urology, Peter MacCallum Cancer Centre, Melbourne, Australia
Written by: Rashid K. Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2023 European Association of Urology (EAU) 38th annual congress held in Milan, Italy between March 10-13, 2023
References:
- Emmett et al. The Additive Diagnostic Value of Prostate-specific Membrane Antigen Positron Emission Tomography Computed Tomography to Multiparametric Magnetic Resonance Imaging Triage in the Diagnosis of Prostate Cancer (PRIMARY): A Prospective Multicentre Study. Eur Urol, 2021. 80(6):682-689.
- Emmett et al. The PRIMARY Score: Using Intraprostatic 68Ga-PSMA PET/CT Patterns to Optimize Prostate Cancer Diagnosis. J Nucl Med, 2022. 63(11):1644-1650.