ASCO GU 2023: Predictive and Prognostic Potential of Pretreatment 68Ga-PSMA PET Tumor Heterogeneity Index in Patients with mCRPC

( The 2023 GU ASCO annual meeting included a session on prostate cancer, featuring a presentation by Dr. Vikas Prasad discussing the predictive and prognostic potential of pretreatment 68Ga-PSMA PET tumor heterogeneity index in patients with metastatic castration-resistant prostate cancer (mCRPC). 177Lu-PSMA therapy has been introduced as an effective therapeutic option for mCRPC. Since about one third of the treated patients show no biochemical response after therapy, prediction of treatment outcome is important for patient selection. Therefore, this study was conducted to evaluate to the predictive values of volumetric parameters and radiomic features extracted from pretreatment 68Ga-PSMA PET and baseline clinical parameters in response to 177Lu-PSMA therapy.

In this multicenter study, mCRPC patients undergoing 177Lu-PSMA therapy were enrolled from September 2017 to January 2022. The available clinical data of all patients were collected and documented from three different centers. According to the outcome of therapy, the patients were classified into two groups including positive biochemical response (≥ 50% reduction in the serum PSA value) and negative biochemical response (< 50%). Sixty-five radiomic features, eight volumetric parameters and also seventeen clinical parameters were evaluated for prediction of biochemical response. In addition, the impact of such parameters on overall survival was evaluated.

In this retrospective study, 33 prostate cancer patients with a median age of 69 years (range: 49-89) were enrolled. Biochemical response was observed in 22 patients (66%), and 16 patients (48.5%) died during the follow-up time. The results of Spearman correlation test indicated a significant relationship between biochemical response and treatment cycle, administered dose, HISTO energy, GLCM entropy, and GLZLM LZLGE (p<0.05). In addition, according to the Mann-Whitney U test, age, cycle, dose, GLCM entropy, and GLZLM LZLGE were significantly different between biochemical response and non biochemical response patients (p<0.05). According to the ROC curve analysis for feature selection for prediction of biochemical response, GLCM entropy, age, treatment cycle, and administered dose showed acceptable results (p<0.05):

177Lu-PSMA therapy.jpg

According to SVM for the assessing of the best model for prediction of response to therapy, GLCM entropy alone showed the highest predictive performance in treatment planning. For the entire cohort, the Kaplan-Meier test revealed a median overall survival of 21 months (95% CI 12.12-29.88). The median overall survival was estimated at 26 months (95% CI 17.43-34.56) for biochemical response patients and 13 months (95% CI 9.18-16.81) for non biochemical response patients. Among all variables included in the Kaplan Meier analysis, only response to therapy was statistically significant (p =0.01) and none of the radiomic features and other clinical factors achieved a p-value of less than 0.05.

Dr. Prasad concluded his presentation discussing the predictive and prognostic potential of pretreatment 68Ga-PSMA PET tumor heterogeneity index in patients with mCRPC with the following take-home messages:

  • This exploratory study showed that heterogeneity parameter of pretreatment 68Ga-PSMA PET images might be a potential predictive value for response to 177Lu-PSMA therapy in mCRPC
  • Further prospective studies need to be carried out to verify these findings

Presented by: Vikas Prasad, MD, PhD, University Hospital Ulm, Ulm, Germany

Co-Authors: Majid Assadi, Reyhaneh Manafi-Farid, Esmail Jafai, Ahmad Keshavarz, GhasemAli Divband, Mohammad Mobin Moradi, Zohreh Adinehpour, Rezvan Samimi, Habibollah Dadgar, Benjamin Mayer

Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2023 Genitourinary (GU) American Society of Clinical Oncology (ASCO) Annual Meeting, San Francisco, Thurs, Feb 16 – Sat, Feb 18, 2023.