(UroToday.com) The 2023 Society of Nuclear Medicine and Molecular Imaging (SNMMI) Annual Meeting held in Chicago, IL between June 24th and 27th, 2023 was host to a prostate cancer session. Dr. Jinhui Yang presented the results of an analysis evaluating the role of 68Ga-PSMA PET/CT-based multivariable modeling for the diagnosis of clinically significant prostate cancer (csPCa) in patients with PSA levels in the 4-10 ng/ml range.
PSMA-PET/CT is currently approved for the initial staging of prostate cancer patients prior to treatment and for those with biochemical recurrence following primary, definitive therapy. There has been an increased interest in evaluating the role of PSMA-PET/CT in the initial diagnostic setting, with the PRIMARY trial demonstrating that the combinatory approach of a csPCa from 83% to 97%. The PRIMARY trial further demonstrated that the probability of csPCa increased exponentially as the SUVmax increased from 2.5 to 10, with the probability of csPCa leveling off at 1.0 for lesions/patients with SUVmax of 10 or greater.1
Patients with PSA levels in the 4-10 range are often considered to be in the PSA ‘gray zone’, with numerous patients in this setting undergoing systematic, non-targeted biopsies having no evidence of csPCa. As such, the objective of this study was to evaluate whether 68Ga-PSMA-PET/CT parameters, such as the maximum standardized uptake value (SUVmax), combined with other clinical parameters, can be used to predict the odds of csPCa in patients with a PSA of 4-10 ng/ml.
This study included patients with a total serum PSA level of 4 – 10 ng/ml, who underwent an mpMRI, 68Ga-PSMA PET/CT, and systematic and targeted prostate biopsies. Patients were stratified based on their biopsy results into either a csPCa or non-csPCa group, and the following clinical parameters were compared between the two groups:
- PSA level
- Prostate volume
- PSA density
- Free/total PSA ratio
- Prostate Imaging-Reporting and Data System version 2.1 (PI-RADS v2.1) score
- 68Ga-PSMA-PET/CT imaging evaluation results
- SUVmax
The investigators analyzed the association between SUVmax and odds of csPCa using multivariable logistic regression analysis, adjusted for the evaluable clinical parameters, and subsequently established a predictive model based on SUVmax that was evaluated by analyzing the receiver operating characteristic (ROC) curve and decision curve analysis (DCA)
Eighty-one patients were included, 29 (36%) of who had evidence of csPCa on prostate biopsy. Among the 29 patients with csPCa, 25 (86.2%) had a positive MRI test, and 27 (93%) had a positive 68Ga-PSMA-PET/CT scan. Conversely, only 56% and 23% of patients without csPCa had a positive MRI or PSMA-PET/CT scan. Compared to patients without csPCa, those with csPCa had:
- Smaller prostatic volumes
- Lower free/total PSA ratios
- Higher PSA densities
- Higher SUV max (p for all <0.05)
Using the univariable screening approach for multivariable modeling, the authors included the significant variables on univariable analysis in the multivariable logistic regression model. Given the collinearity of prostatic volume and PSA density, PSA density was not included in the multivariable model, which included prostatic volume, free/total PSA ratio, and SUVmax.
On multivariable analysis, a higher SUVmax was associated with significantly increased odds of csPCa (OR: 1.73, 95% CI: 1.33 – 2.25). Prostatic volume and free to total ratio were both also significantly associated with the odds of csPCa. Next, an SUVmax-based prediction model for csPCa was built, incorporating all three variables of interest.
ROC analysis demonstrated that the multivariable model incorporating all three variables outperformed each of the three individual variables (area under the curve: 0.93 versus 0.59 – 0.85). The diagnostic sensitivity and specificity of the prediction model were 86.2% and 86.5%, respectively. DCA demonstrated that 68Ga-PSMA PET/CT and the prediction model had comparable and obviously higher net benefits, compared to the other diagnostic methods for risk thresholds of 10%-40%. For risk thresholds ≥40%, the net benefit of the prediction model was greater than that of 68Ga-PSMA PET/CT and the other clinical variables. As such, DCA demonstrated that the clinical utility of 68Ga-PSMA PET/CT and the prediction model were superior to that of mpMRI and PSA on most occasions.
Based on these results, Dr. Yang and colleagues concluded that a new prediction model based on 68Ga-PSMA-PET/CT SUVmax, prostatic volume, and free to total PSA ratio can improve the discriminatory performance for csPCa in patients with serum total PSA levels of 4 to 10 ng/ml. Utilization of this prediction model may minimize unnecessary prostate biopsy procedures in this setting and lead to improved detection of csPCa.
Presented by: Jinhui Yang, MD, Department of Nuclear Medicine, Xiangya Hospital, Central South University, Changsha, China.
Written by: Rashid K. Sayyid, MD, MSc – Society of Urologic Oncology (SUO) Clinical Fellow at The University of Toronto, @rksayyid on Twitter during the 2023 Society of Nuclear Medicine and Molecular Imaging (SNMMI) Annual Meeting, Chicago, IL, Sat, June 24 – Tues, June 27, 2023.
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