The diagnostic benefit of ${}^{68}$Ga-PSMA-HBED-CC PET/CT in the primary diagnosis of prostate carcinoma

Prostate carcinoma is the second most common new cancer in men in Germany. Primary diagnostics are crucial for therapy planning. However, the imaging currently used shows high interobserver variability as well as low sensitivities or moderate specificities. PET/CT with the ${}^{68}$gallium-labelled ligand of the prostate-specific membrane antigen (${}^{68}$Ga-PSMA-HBED-CC PET/CT) was able to localise prostate carcinoma with high accuracy in previous studies. The aim of this retrospective study was therefore to investigate the accuracy of ${}^{68}$Ga- PSMA PET/CT in primary diagnosis. For this purpose, a study cohort (n = 47) with bioptically confirmed prostate carcinoma without previous therapy was analysed. In the total group, the maximum standardised uptake value (SUV${}_{max}$) of the prostate was correlated with the bioptic Gleason score and the prostate-specific antigen in the serum. No significant correlations were found here. A subgroup (n = 21) underwent prostatectomy a median of 4 days after PET/CT imaging. Based on a predefined 6-segment model, the segmental tumour burden in this group was determined histopathologically and in PET/CT by different cut-off values and correlated with each other. In addition, the infiltration of the seminal vesicles and the extracapsular growth were analysed. Histopathologically tumour-free segments had a significantly lower SUV${}_{max}$ (4.9 ± 2.9; n = 26 of 100, 21 %) than affected segments (11.8 ± 7.6; n = 100 of 126, 79 %) on PET/CT. Receiver operating characteristic analysis yielded an area under the curve (AUC) of 0.84 for an optimal SUV${}_{max}$ cut-off of 6.5 to distinguish between histopathologically positive and negative segments. This resulted in a specificity of 92%, a sensitivity of 67%, a positive predictive value of 97% and a negative predictive value of 42%. Segmental tumour burden determined in PET/CT by the formula 2 × SUV${}_{blood}$ + 2 × standard deviation correlated best with histopathology (Pearson ρ = 0.68, p = < 0.001, mean ± SA: 19 % ± 15 %). The ${}^{68}$Ga-PSMA PET/CT detected seminal vesicle infiltration with 86 % accuracy (n = 11, 52 %) and cross-capsular tumour growth with 86 % accuracy (n = 12, 57 %). In summary, ${}^{68}$Ga-PSMA PET/CT reliably determined localisation and tumour extension of prostate cancer in the primary diagnostic setting. The data from this group of patients encourage the conduct of prospective studies on PET-guided biopsy sampling to optimally guide treatment decisions.