The relationship between mpMRI-TB and CB has long been a subject worthy of discussion. And increasing investigations are exploring the possible approaches to reduce the systematic biopsy cores[24–27]. In our study, PSMA PET derived SUVmax and mpMRI derived ADCmin were found to be independent risk factors for the prediction of concordance between TB and CB. The biopsy concordance means mono-TB can reflect the accurate pathological grade without SB at all. Therefore, the present study revealed that undergoing 68Ga-PSMA-11 PET/CT and mpMRI prior to prostate biopsy can avoid unnecessary systematic biopsy cores and potentially risky procedure. To our knowledge, this is the first study to explore the role of 68Ga-PSMA-11 PET/CT and ADC value to predict the biopsy concordance between mpMRI-TB and CB to recommend mono-TB in prostate biopsy.
In this study, SUVmax was significantly decreased in patients with biopsy concordance (Table 3). PSMA is a transmembrane glycoprotein expressed on the cell membrane. Compared with normal prostate tissue or benign prostatic hyperplasia, PSMA showed a specific high expression pattern in PCa. In the reported studies, the expression of PSMA increased with tumor lesions with higher Gleason score[28] and SUVmax was positively correlated with tumor grade[29]. Therefore, our result can be explained that the expression of PSMA is related to the malignancy degree, invasiveness and heterogeneity of the tumor, the higher the expression of SUVmax, the higher the heterogeneity of the tumor, and a few small tumor lesions do not perform on the mpMRI, so mpMRI-TB fails to reach the highest tumor grade of the specimen which is reached by extensive SB, which leads to the biopsy discordance. On the contrary, the lower the expression of SUV, the lower the heterogeneity of the tumor, and the more uniform the histopathologic grade inside the tumor lesions. In this case, the tumor grade of tumor specimen with mpMRI-TB is concordant with that with SB or higher than that of the normal tissue or hyperplastic tissue biopsied by SB, which is defined as biopsy concordance. According to our results, these patients can undergo mono-TB without SB at all.
ADCmin was also found to be an independent risk factor for prediction of biopsy concordance. The apparent diffusion coefficient (ADC), derived from diffusion-weighted MRI, is thought to be related to the cellularity and interstitial structure of pathological tissue. In PCa, normal glandular epithelial and tubular structures are damaged, proliferating, dense cancer cells replace the normal acinar structures, and the diffusion of water molecules would be limited, resulting in lower ADC values. Therefore, ADC can reflect the histopathological heterogeneity of malignant tumors[30–32]. In the reported studies, Peng, etc.[33] found ADC10 and ADCmean can distinguish prostate cancer from normal tissue. Donati et al.[34] evaluated the relation between different ADC values and Gleason scores, and found the most significant relation between ADC10 and Gleason scores, but patients in their cohort only underwent mpMRI-TB to perform the pathological findings. In our investigation, ADCmin could recommend patients underwent mono-TB by comparing the pathological findings between mpMRI-TB and CB.
Generally, our findings revealed that, for PI-RADS 4 and 5 on mpMRI, patients with lower SUVmax and higher ADCmin had the strongest probability for biopsy concordance ((Fig. 2). Therefore, 68Ga-PSMA-11 PET/CT combined with mpMRI might be helpful to select the biopsy approach before prostate biopsy. Based on the results, mpMRI-TB could be considered for patients with lower SUVmax and higher ADCmin to decrease unnecessary biopsy cores, potential physical hazards.
There are also several limitations in this investigation. Firstly, this is a single-center retrospective study and the sample size is only 115 patients, the results of multivariable analysis may be affected. Therefore, our findings need to be further verified by a larger external cohort. Secondly, patients without suspicious lesion on mpMRI (PI-RADS 1,2 and 3) were not considered in this investigation due to the low cancer detection rate by mpMRI-TB. A meta-analysis revealed that the prevalence of PI-RADS 3 cases was 17.3%, with similar rates of csPCa (19%) and insignificant PCa (17%) cases. Therefore, PI-RADS 3 lesions are recognized as equivocal for the presence of csPCa and not defined as positive lesions[35–37], therefore, The guiding role of 68Ga-PSMA-11 PET/CT combined with mpMRI for these patients remains unclear. Thirdly, not all the pathological diagnosis of final radical prostatectomy specimens is known. Therefore, there is no evaluation of correlation between biopsy and final radical prostatectomy specimens.
To sum up, the biopsy concordance of findings substantiates the conclusion: 68Ga-PSMA-11 PET/CT combined with mpMRI prior to prostate biopsy can be an ideal risk factor of PCa to guide the clinicians and patients to consider the appropriate biopsy approach-mono-TB without additional SB. The prediction deserves special consideration and is a subject worthy of future evaluation. Moreover, we need more further prospective studies to validate our findings.