External validation of nomograms including MRI features for the prediction of side-specific extraprostatic extension

BACKGROUND

Prediction of side-specific extraprostatic extension (EPE) is crucial in selecting patients for nerve-sparing radical prostatectomy (RP). Multiple nomograms, which include magnetic resonance imaging (MRI) information, are available predict side-specific EPE. It is crucial that the accuracy of these nomograms is assessed with external validation to ensure they can be used in clinical practice to support medical decision-making.

METHODS

Data of prostate cancer (PCa) patients that underwent robot-assisted RP (RARP) from 2017 to 2021 at four European tertiary referral centers were collected retrospectively. Four previously developed nomograms for the prediction of side-specific EPE were identified and externally validated. Discrimination (area under the curve [AUC]), calibration and net benefit of four nomograms were assessed. To assess the strongest predictor among the MRI features included in all nomograms, we evaluated their association with side-specific EPE using multivariate regression analysis and Akaike Information Criterion (AIC).

RESULTS

This study involved 773 patients with a total of 1546 prostate lobes. EPE was found in 338 (22%) lobes. The AUCs of the models predicting EPE ranged from 72.2% (95% CI 69.1-72.3%) (Wibmer) to 75.5% (95% CI 72.5-78.5%) (Nyarangi-Dix). The nomogram with the highest AUC varied across the cohorts. The Soeterik, Nyarangi-Dix, and Martini nomograms demonstrated fair to good calibration for clinically most relevant thresholds between 5 and 30%. In contrast, the Wibmer nomogram showed substantial overestimation of EPE risk for thresholds above 25%. The Nyarangi-Dix nomogram demonstrated a higher net benefit for risk thresholds between 20 and 30% when compared to the other three nomograms. Of all MRI features, the European Society of Urogenital Radiology score and tumor capsule contact length showed the highest AUCs and lowest AIC.

CONCLUSION

The Nyarangi-Dix, Martini and Soeterik nomograms resulted in accurate EPE prediction and are therefore suitable to support medical decision-making.

Consecutive PSMA and AR PET imaging shows positive correlation to AR and PSMA protein expression in primary hormone naïve prostate cancer

Rationale: The present study set out to investigate if PET imaging can be used as a potential substitute for immunohistochemical analysis of tumor samples in prostate cancer (PC) patients. Correlation between imaging signals of two PET tracers and the corresponding target structures was assessed. The first tracer was [⁶⁸Ga]Ga-PSMAHBED-CC([⁶⁸Ga]PSMA), which is already implemented in clinical routine. The second tracer was [¹⁸F]-fluoro-5α-dihydrotestosterone([¹⁸F]FDHT) which binds to the androgen receptor (AR). The AR is particularly interesting in PC, since the AR expression status and its shift during therapy might directly influence patient care. Methods: This prospective, explorative clinical study included 10 newly diagnosed PC patients. Each patient received a [⁶⁸Ga]PSMA-PET/MRI- and [¹⁸F]FDHT-PET/MRI-scan prior to prostatectomy. Cancer standardized uptake values (SUV) were determined and related to background SUVs. Following prostatectomy, tumor tissue was sampled and AR and prostate-specific membrane antigen (PSMA) expression determined. AR and PSMA expressions were evaluated quantitively with QuPath and additionally with a four-tiered rating system. Correlation between imaging signals and marker expression was statistically assessed. Results: For [¹⁸F]FDHT, the SUV_max/SUVbackground ratio showed a significant, strong correlation (P-value=0.019, r=0.72) with AR optical density of the correlating tissue sample. The correlation between PSMA optical density and the [⁶⁸Ga]PSMA SUV_max/SUVbackground ratio was not significant (P-value=0.061), yet a positive correlation trend could be observed (r=0.61). SUV_max/SUVbackground ratios were higher for [⁶⁸Ga]PSMA (34.9±24.8) compared to [¹⁸F]FDHT (4.8±1.2). In line with this findings, the tumor detection rate of the Ga-PSMA-PET scan was 90%, but only 40% for the [¹⁸F]FDHT-PET scan. The four-tiered rating of PSMA staining intensity yielded very homogenous results with values of 3+ for most subjects (90%). The AR staining was rated with 1+ in two patients (20%), with 2+ in four patients (40%) and with 3+ in four patients (40%). Conclusion: [¹⁸F]FDHT-PET may be useful for monitoring AR expression and alterations of AR expression during treatment of PC patients. This may facilitate early detection of treatment resistance and allows for adaptation of therapy to prevent cancer progression. [¹⁸F]FDHT-PET is inferior to [⁶⁸Ga]PSMA-PET for primary PC diagnosis, but the correlation between [⁶⁸Ga]PSMA SUVs and PSMA expression is weaker compared to [¹⁸F]FDHT and the AR.