A post-hoc analysis of the PRIMARY study sought to assess the clinical significance of patterns of intra-prostatic PSMA activity, proposing a 5- point PRIMARY score to optimize accuracy of PSMA-PET/CT for csPCa in a low prevalence prostate cancer population. The results were published in the Journal of Nuclear Medicine.
This study analyzed the aforementioned PRIMARY trial, a prospective multi-center phase II imaging trial that enrolled almost 300 biopsy-naïve men with suspected PCa, no prior biopsy, recent mpMRI (6 months) and planned for prostate biopsy. As the researchers noted, the mpMRI was read separately using PI-RADS (V2). PSMA-PET/CT (pelvic only) was acquired a minimum 60-minute post injection. PSMA-PET/CT was centrally read for pattern (diffuse transition zone (TZ), symmetrical central zone (CZ), focal TZ or peripheral zone (PZ), and intensity (SUVmax).
As part of the post-hoc analysis, a 5-level PRIMARY score was assigned based on analysis of the central read: 1. No pattern, 2. Diffuse TZ or CZ (no focal), 3. Focal TZ, 4. Focal PZ or 5. SUVmax ≥ 12. The researchers then assessed correlations between PRIMARY score and csPCa (ISUP≥2).
In the population of interest, over half (56%) had csPCa. The researchers observed that the PRIMARY score-1 was present in 16% of patients, score-2 in 19% of patients, score-3 in 10% of patients, score-4 in 40% (117) and score-5 in 15% (43). They noted that the proportion of patients with csPCa and PRIMARY score 1 to 5 was 8.5%, 27%, 38%, 76% and 100% respectively. They further noted that sensitivity, specificity, PPV and NPV for PRIMARY score 1,2 (low-risk patterns) vs PRIMARY score 3-5 (high-risk patterns) was 88%, 64%, 76% and 81%, compared to 83%, 53%, 69% and 72% for PI-RADS (2 vs 3-5) on mpMRI.
“A PRIMARY score incorporating intra-prostatic pattern and intensity on PSMA-PET/CT shows potential with high diagnostic accuracy for csPCa. Further validation is warranted prior to implementation,” the researchers concluded.