PET/MRI helped avoid unnecessary biopsies in prostate cancer diagnosis
Chinese researchers conducted a small clinical trial and found that PET/MRI can accurately differentiate ambiguous cases of suspected prostate cancer, sparing patients from unnecessary biopsies. A report of the work is published in the Journal of Nuclear Medicine.
European guidelines currently recommend performing multiparametric MRI (mpMRI) of the prostate before biopsy because of its good sensitivity in detecting clinically significant cancer of this organ. The five-stage PI-RADS scale is used to standardise this examination and to assess tumour likelihood. The greatest diagnostic challenge is the PI-RADS gradation 3, which corresponds to a medium probability (clinically significant cancer is doubtful, presence is ambiguous). Biopsy is recommended, although a clinically significant neoplasm can be detected in less than 20 per cent of cases. Additional PET/CT with prostate-specific membrane antigen labelled with radioactive gadolinium-68 (CT) can improve the quality of diagnosis.
Given these data, Hongqian Guo from Nanjing University and colleagues decided to test the diagnostic efficacy of 68Ga-PSMA PET/MRI, which accurately records anatomical localisation simultaneously with radiological data, for the diagnosis of PI-RADS 3 lesions in prospective clinical trials (NCT 04573179). They included 56 men with single or multiple PI-RADS 3 graded prostate lesions identified by mpMRI within the previous three months. They did not undergo biopsy.
During the study, participants were injected intravenously with 68Ga-PSMA-11 with an activity of 111-185 (median 142) megabecquerels. About an hour later, they underwent PET/MRI - first of the whole body, then separately of the pelvis. Image reconstruction was performed time-of-flight and using an iterative algorithm of expected maximisation of ordered subsets. The images were evaluated using the PRIMARY five-point system by two independent experienced nuclear medicine specialists who were unaware of previous mpMRI findings and the clinical characteristics of the patients. All patients then underwent multifocal 12-point and targeted (mpMRI/ultrasound guided) prostate biopsy for comparison of imaging and histological data. Statistical processing of the results was performed descriptively and by ROC curve.
Clinically significant prostate cancer was found in eight (14.3 per cent) participants. Their proportion with PRIMARY scores of 1, 2, 3, 4 and 5 were 0 per cent (0/12); 0 per cent (0/13); 6.3 per cent (1/16); 38.5 per cent (5/13) and 100 per cent (2/2), respectively. The calculated area under the ROC curve was 0.91 (95 per cent confidence interval 0.817-0.999). For 4-5 versus 1-3 PRIMARY scores, the sensitivity, specificity, positive and negative predictive value were 87.5; 83.3; 46.7 and 97.5 per cent, respectively.
If at least 4 PRIMARY scores were used to make a decision about biopsy at PI-RADS 3, 40 of 48 participants without clinically significant prostate cancer could avoid this intervention, but 1 of 8 would have no detectable disease, the authors of the paper noted. 68Ga-PSMA PET/MRI has great potential to diagnose prostate cancer at PI-RADS 3 and may help avoid unnecessary biopsies, they said.
An earlier meta-analysis by a European collaboratory showed that MRI should be included in prostate cancer screening. In turn, British researchers have demonstrated that even a single invitation to men for screening of prostate-specific antigen levels reduces the risk of death from this disease.