Potential synergistic implications for stromal-targeted radiopharmaceuticals in bone-metastatic prostate cancer

Therapeutic efficacy, prognostic variables and clinical outcome of 177Lu-PSMA-617 PRLT in progressive mCRPC following multiple lines of treatment: prognostic implications of high FDG uptake on dual tracer PET-CT vis-à-vis Gleason score in such cohort

OBJECTIVE

To evaluate the therapeutic response, progression free survival (PFS), overall survival (OS) and clinical toxicity of ¹⁷⁷Lu-PSMA-617 PSMA targeted radioligand therapy (PRLT) in the setting of heavily pre-treated metastatic castrate-resistant prostate cancer (mCPRC) patients and also examine the association of prognostic variables with therapeutic outcome in such patient cohort.

METHODS

We examined the medical records of mCRPC patients who had undergone ¹⁷⁷Lu-PSMA-617 PRLT from March 2017 to February 2019 in our institute. Patients receiving equal to or more than two cycles were included and analyzed in this retroprospective study.The ⁶⁸Ga-PSMA-11 PET-CT and 18-fludeoxyglucose positron emission tomography (¹⁸FDG PET)-CT scan findings, serum prostate-specific antigen (PSA) change, health-related quality of life (HRQoL) scales (Eastern Cooperative Oncology Group/Karnofsky score) and Gleason score were assessed for their implications on the outcome of therapy. The treatment response was evaluated under three categories: (a) symptomatic (b) biochemical and (c) imaging response.The PFS and OS following first PRLT were determined and the association of various variables with PSA doubling time (DT) and FDG uptake in the lesions were analyzed. Toxicity assessment was undertaken objectively by National Cancer Institute-Common Terminology Criteria for Adverse Events scale v. 5.0 for haematological and nephrotoxicity, and salivary gland toxicity assessed by xerostomia inventory score.

RESULTS

A total of 40 mCRPC patients (age range: 46-84 years; median 63 years), who had undergone ¹⁷⁷Lu-PSMA-617 PRLT, of at least two cycles was identified and selected for the analysis. FDG uptake was noted in 87.5% of patients (n = 35). Out of 40 cases, 21 were responders (CR, PR and SD) and 19 were non-responders (PD) on symptomatic and biochemical scales while on molecular imaging response, 16 (43%) were responders and remaining 21 (57%) were non-responders. Lesion-wise, ⁶⁸Ga-PSMA-11 avid metastatic nodal disease responded well with ¹⁷⁷Lu PSMA-617 PRLT, as compared to hepatic and skeletal lesions. The median OS and PFS was 12 and 7 months respectively following first PRLT. Patients with negative serum PSA-DT demonstrated superior 1 year PFS as compared to those with positive serum PSA-DT (52.5 vs 47.5%) (p = 0.029). Patients receiving greater than two cycles PRLT demonstrated a higher negative PSA-DT as compared to those receiving two cycles (p-value = 0.03). Grade 1 xerostomia was observed in two patients (5%) (mean xerostomia score of 23), haematotoxicity in seven patients [Grade I (n = 2, 5%) and Grade II (n = 5, 14%)].

CONCLUSION

¹⁷⁷Lu-PSMA-617 PRLT was well-tolerated and able to produce disease control with good symptomatic and biochemical responses in the context of heavily pre-treated mCRPC with progressive disease, with low toxicity profile. Evident association of high FDG uptake was observed with aggressive disease biology coupled with increasing Gleason score and poorer 12 months PFS. Negative PSA-DT following therapy demonstrated longer PFS. The results demonstrate important future role of ¹⁷⁷Lu-PSMA-617 PRLT in the treatment of mCRPC.

ADVANCES IN KNOWLEDGE

The present work explored in a large teriary cancer care setting, the efficacy of ¹⁷⁷Lu-PSMA-617 PRLT, in an aggressive and unselected subset of mCRPC. The response and outcome was correlated with a number of prognostic variables, including molecular imaging findings (FDG uptake in the metastatic lesions), PSA DT and Gleason score.

Alpha emitter radium-223 and survival in metastatic prostate cancer

BACKGROUND

Radium-223 dichloride (radium-223), an alpha emitter, selectively targets bone metastases with alpha particles. We assessed the efficacy and safety of radium-223 as compared with placebo, in addition to the best standard of care, in men with castration-resistant prostate cancer and bone metastases.

METHODS

In our phase 3, randomized, double-blind, placebo-controlled study, we randomly assigned 921 patients who had received, were not eligible to receive, or declined docetaxel, in a 2:1 ratio, to receive six injections of radium-223 (at a dose of 50 kBq per kilogram of body weight intravenously) or matching placebo; one injection was administered every 4 weeks. In addition, all patients received the best standard of care. The primary end point was overall survival. The main secondary efficacy end points included time to the first symptomatic skeletal event and various biochemical end points. A prespecified interim analysis, conducted when 314 deaths had occurred, assessed the effect of radium-223 versus placebo on survival. An updated analysis, when 528 deaths had occurred, was performed before crossover from placebo to radium-223.

RESULTS

At the interim analysis, which involved 809 patients, radium-223, as compared with placebo, significantly improved overall survival (median, 14.0 months vs. 11.2 months; hazard ratio, 0.70; 95% confidence interval [CI], 0.55 to 0.88; two-sided P=0.002). The updated analysis involving 921 patients confirmed the radium-223 survival benefit (median, 14.9 months vs. 11.3 months; hazard ratio, 0.70; 95% CI, 0.58 to 0.83; P<0.001). Assessments of all main secondary efficacy end points also showed a benefit of radium-233 as compared with placebo. Radium-223 was associated with low myelosuppression rates and fewer adverse events.

CONCLUSIONS

In this study, which was terminated for efficacy at the prespecified interim analysis, radium-223 improved overall survival. (Funded by Algeta and Bayer HealthCare Pharmaceuticals; ALSYMPCA ClinicalTrials.gov number, NCT00699751.).