AUA 2022: Reliability of 68Ga-PSMA PET/CT in Assessing Real Nodal Burden in Men With cN1 Disease: Clinical Implications for Patient Counselling and Multi-Modal Treatments

(UroToday.com) In a moderated poster presentation at the 2022 American Urologic Association Annual Meeting held in New Orleans and virtually, Dr. Stabilie presented on the clinical implications of 68Ga-Prostate Specific Membrane Antigen (PSMA)-PET/CT to quantify nodal disease burden in patients with cN1 disease. Previous work has shown that 68-Ga PSMA PET/CT has good accuracy in the primary staging of prostate cancer and localization of biochemically recurrent disease. In the recurrent setting, previous studies have shown a correlation between tumor burden and the risk of PET underestimation.

However, this has yet to be assessed in the setting of primary staging which the authors sought to do in this work.

To address this question, the authors identified 90 patients who underwent 68Ga-PSMA PET/CT before RP and extended lymph node dissection between 2019 and 2021 at two centers. They assessed the primary outcome of tumor underestimation, defined as the difference between the number of positive nodes at pathology and the number of positive nodal spots detected on PSMA PET/CT. This association, between number of positive spots at PSMA PET and underestimation of tumor burden, was further assessed on multivariable linear. The continuous interaction between preoperative PSA and number of positive spots and the probability of tumor underestimation was graphically explored through an heatmap.

At the time of imaging, the median PSA was 9 ng/ml (IQR 5-16 ng/ml). Among the included patients, 30 patients (32%) had positive nodal spots at PSMA PET and 32 (35%) had histologically confirmed positive nodes.

Among those with radiographic evidence of disease in nodal distributions on PSMA PET, 19/30 (63%) had pN1 disease with a specificity of 81%. Among patients with positive PET, the median number of positive spots was 2 (IQR 1-3). PSMA PET underestimated the burden of nodal invasion in 22 of 30 men with positive spots (73%). Patients with underestimated nodal burden had higher rate of PSA persistence (36%) compared with those without underestimation (11%). In linear regression analyses, higher number of positive PSMA nodal lesions was associated with increased risk of underestimating tumoral burden (OR 1.05, p=0.02). When graphically explored, the underestimation rate progressively increased with higher PSA level and higher tumor burden at PET. 

Thus, the authors conclude that 68Ga-PSMA PET underestimates the real tumor burden in men with cN1 disease. This risk increases with an increasing number of PSMA lesions and higher PSA level.