The Prognostic Value of Posttreatment 68Ga-PSMA-11 PET/CT and 18F-FDG PET/CT in Metastatic Castration-Resistant Prostate Cancer Treated with 177Lu-PSMA-617 and NOX66 in a Phase I/II Trial (LuPIN).

177Lu-PSMA-617 therapy has shown high prostate-specific antigen (PSA) response rates in men with metastatic castration-resistant prostate cancer. However, early treatment resistance is common. This LuPIN substudy aimed to determine the prognostic value of posttreatment quantitative PET for PSA progression-free survival (PFS) and overall survival (OS) with 177Lu-PSMA-617 therapy. Methods: Fifty-six men with progressive metastatic castration-resistant prostate cancer were enrolled in the LuPIN trial and received up to 6 doses of 177Lu-PSMA-617 and a radiation sensitizer (NOX66). 68Ga-PSMA-11 and 18F-FDG PET/CT, diagnostic CT, and bone scanning were performed at study entry and exit. Quantitative analysis tracked change in total tumor volume (TTV) and SUV. Univariable and multivariable analyses were conducted to examine the association of change in TTV (continuous and >30%), SUVmax, PSA, and radiographic progression with PSA PFS and OS. Results: All men (37/56) who underwent both screening and posttreatment molecular imaging were analyzed; 70% (26/37) had a PSA response of more than 50%. Median PSA PFS was 8.6 mo, and median OS was 22 mo. Clinical progression had occurred at trial exit in 54% (20/37). In response to treatment, a reduced PSMA SUVmax was demonstrated in 95% (35/37) and a reduced PSMA TTV in 68% (25/37). An increase in PSMA TTV by at least 30% was associated with worse OS (median, 10.2 vs. 23.6 mo; P = 0.002). Change in PSMA SUVmax was not associated with PSA PFS or OS. 18F-FDG SUVmax was reduced in 51% (18/35) and 18F-FDG TTV in 67% (22/35). An increased 18F-FDG SUVmax was associated with worse OS (median, 20.7 vs. 25.7 mo; P < 0.01). An 18F-FDG TTV increase by more than 30% was associated with a short PSA PFS (median, 3.5 vs. 8.6 mo; P < 0.001) but not OS. Both PSA and radiographic progression were associated with shorter OS (median, 14.5 vs. 25.7 mo [P < 0.001] and 12.2 vs. 23.6 mo [P = 0.002]). On multivariable analysis, only increased PSMA TTV and PSA progression remained independently prognostic of OS (hazard ratio, 5.1 [95% CI, 1.5-17.1; P = 0.008] and 3.5 [95% CI, 1.1-10.9; P = 0.03], respectively). Conclusion: Change in quantitative PSMA TTV has strong potential as a prognostic biomarker with 177Lu-PSMA-617 therapy, independent of 18F-FDG PET parameters, PSA, or radiographic progression. Further research into the value of posttreatment PET as an imaging biomarker is warranted.

177Lu-PSMA SPECT Quantitation at 6 Weeks (Dose 2) Predicts Short Progression-Free Survival for Patients Undergoing 177Lu-PSMA-I&T Therapy.

177Lu-PSMA is an effective treatment in metastatic castration-resistant prostate cancer (mCRPC). Our ability to assess response rates and adjust treatment may be improved using predictive tools. This study aimed to evaluate change in 177Lu-PSMA SPECT quantitative parameters to monitor treatment response. Methods: One hundred twenty-seven men with progressive mCRPC previously treated with androgen-signaling inhibition (99%) and chemotherapy (71%) received a median of 3 (interquartile range [IQR], 2-5) 8-GBq (IQR, 8-8.5 GBq) doses of 177Lu-PSMA-I&T. Imaging included 68Ga-PSMA-11 PET/CT (SUVmax > 15 at a single site and > 10 at all sites > 2 cm), diagnostic CT, and 177Lu SPECT/CT from vertex to mid thigh (24 h after treatment). 177Lu SPECT/CT quantitative analysis was undertaken at cycles 1 (baseline) and 2 (week 6) of treatment. Clinical and biochemical results were assessed to evaluate prostate-specific antigen (PSA) progression-free survival (PFS) and overall survival (OS). Results: A PSA reduction of more than 50% was seen in 58% (74/127). The median PSA PFS was 6.1 mo (95% CI, 5.5-6.7), and OS was 16.8 mo (95% CI, 13.5-20.1). At the time of analysis, 41% (52/127) were deceased. At baseline and week 6, 76% (96/127) had analyzable serial 177Lu SPECT/CT imaging. SPECT total tumor volume (TTV) was reduced between baseline and week 6 in 74% (71/96; median, -193; IQR, -486 to -41). Any increase in SPECT TTV between baseline and week 6 was associated with significantly shorter PSA PFS (hazard ratio, 2.5; 95% CI, 1.5-4.2; P = 0.0008) but not OS. Median PSA PFS in those with an increase in SPECT TTV was 3.7 mo (95% CI, 2.8-6.8), compared with 6.7 mo (95% CI, 5.8-10.6) in those with no increase in SPECT TTV. An increase in SPECT TTV greater than 20% was also associated with PSA PFS (hazard ratio, 1.9; 95% CI, 1.2-3.0; P = 0.008) but less significantly than any change in SPECT TTV. There was a significant difference in PSA PFS between patients with both increased PSA and SPECT TTV and patients with reduced SPECT TTV and PSA (median, 2.8 vs. 9.0 mo; P < 0.0001). Conclusion: Increasing PSMA SPECT TTV on quantitative 177Lu SPECT/CT predicts short progression-free survival and may play a future role as an imaging response biomarker, identifying when to cease or intensify 177Lu-PSMA therapy.

Evaluation of 177Lu-PSMA-617 SPECT/CT Quantitation as a Response Biomarker Within a Prospective 177Lu-PSMA-617 and NOX66 Combination Trial (LuPIN).

177Lu-PSMA-617 is an effective and novel treatment in metastatic castration-resistant prostate cancer (mCRPC). Our ability to assess response rates and therefore efficacy may be improved using predictive tools. This study investigated the predictive value of serial 177Lu-PSMA-617 SPECT/CT (177Lu SPECT) imaging in monitoring treatment response. Methods: Fifty-six men with progressive mCRPC previously treated with chemotherapy and novel androgen signaling inhibitor were enrolled into the LuPIN trial and received up to 6 doses of 177Lu-PSMA-617 and a radiation sensitizer (3-(4-hydroxyphenyl)-2H-1-benzopyran-7-ol [NOX66]). 68Ga-PSMA-11 and 18F-FDG PET/CT were performed at study entry and exit, and 177Lu SPECT from vertex to mid thighs was performed 24 h after each treatment. SPECT quantitative analysis was undertaken at cycles 1 (baseline) and 3 (week 12) of treatment. Results: Thirty-two of the 56 men had analyzable serial 177Lu SPECT imaging at both cycle 1 and cycle 3. In this subgroup, median prostate-specific antigen (PSA) progression-free survival (PFS) was 6.3 mo (95% CI, 5-10 mo) and median overall survival was 12.3 mo (95% CI, 12-24 mo). The PSA 50% response rate was 63% (20/32). 177Lu SPECT total tumor volume (SPECT TTV) was reduced in 68% (22/32; median, -0.20 m3 [95% CI, -1.4 to -0.001]) and increased in 31% (10/32; median, 0.36 [95% CI, 0.1-1.4]). Any increase in SPECT TTV was associated with shorter PSA PFS (hazard ratio, 4.1 [95% CI, 1.5-11.2]; P = 0.006). An increase of 30% or more in SPECT TTV was also associated with a shorter PSA PFS (hazard ratio, 3.3 [95% CI, 1.3-8.6]; P =0.02). Tumoral SUVmax was reduced in 91% (29/32) and SUVmean in 84% (27/32); neither was associated with PSA PFS or overall survival outcomes. PSA progression by week 12 was also associated with a shorter PSA PFS (hazard ratio, 26.5 [95% CI, 5.4-131]). In the patients with SPECT TTV progression at week 12, 50% (5/10) had no concurrent PSA progression (median PSA PFS, 4.5 mo [95% CI, 2.8-5.6 mo]), and 5 of 10 men had both PSA and SPECT TTV progression at week 12 (median PSA PFS, 2.8 mo [95% CI, 1.8-3.7 mo]). Conclusion: Increasing SPECT TTV on quantitative 177Lu SPECT predicts a short PFS and may play a future role as an imaging response biomarker.

Prediction of 177Lu-DOTATATE Therapy Outcomes in Neuroendocrine Tumor Patients Using Semi-Automatic Tumor Delineation on 68Ga-DOTATATE PET/CT.

BACKGROUND: Treatment of metastatic neuroendocrine tumors (NET) with 177Lu-DOTATATE peptide receptor radionuclide therapy (PRRT) results in favorable response only in a subset of patients. We investigated the prognostic value of quantitative pre-treatment semi-automatic 68Ga-DOTATATE PET/CT analysis in NET patients treated with PRRT. METHODS: The medical records of 94 NET patients who received at least one cycle of PRRT at a single institution were retrospectively reviewed. On each pre-treatment 68Ga-DOTATATE PET/CT, the total tumor volume (TTV), maximum tumor standardized uptake value for the patient (SUVmax), and average uptake in the lesion with the lowest radiotracer uptake (SUVmin) were determined with a semi-automatic tumor delineation method. Progression-free survival (PFS) and overall survival (OS) among the patients were compared based on optimal cutoff values for the imaging parameters. RESULTS: On Kaplan-Meier analysis and univariate Cox regression, significantly shorter PFS was observed in patients with lower SUVmax, lower SUVmin, and higher TTV. On multivariate Cox regression, lower SUVmin and higher TTV remained predictive of shorter PFS. Only higher TTV was found to be predictive of shorter OS on Kaplan-Meier and Cox regression analyses. In a post hoc Kaplan-Meier analysis, patients with at least one high-risk feature (low SUVmin or high TTV) showed shorter PFS and OS, which may be the most convenient parameter to measure in clinical practice. CONCLUSIONS: The tumor volume and lowest lesion uptake on 68Ga-DOTATATE PET/CT can predict disease progression following PRRT in NET patients, with the former also predictive of overall survival. NET patients at risk for poor outcomes following PRRT can be identified with semi-automated quantitative analysis of 68Ga-DOTATATE PET/CT.