Competition ('Steal' Phenomenon) between [68Ga]Ga-PSMA-11 Uptake in Prostate Tumor Tissue Versus Healthy Tissue

Baseline Imaging Derived Predictive Factors of Response Following [177Lu]Lu-PSMA-617 Therapy in Salvage Metastatic Castration-Resistant Prostate Cancer: A Lesion- and Patient-Based Analysis

Earlier studies have mostly identified pre-therapeutic clinical and laboratory parameters for the prediction of treatment response to [177Lu]Lu-PSMA-617 in metastatic castration resistant prostate cancer patients (mCRPC). The current study investigated whether imaging-derived factors on baseline [68Ga]Ga-PSMA-11 PET/CT can potentially predict the response after two cycles of [177Lu]Lu-PSMA-617 treatment, in a lesion- and patient-based analysis in men with mCRPC. Included patients had histologically proven mCRPC and a [68Ga]Ga-PSMA-11 PET/CT before and after two cycles of [177Lu]Lu-PSMA-617 treatment. The imaging-based response was evaluated on lesion-level (standardized uptake value (SUV) reduction) and patient-level (total lesion PSMA (TL-PSMA) reduction). In the lesion-level analysis, a clear relationship was found between SUVpeak/max and the imaging-based response to [68Ga]Ga-PSMA-11 PET/CT (most avid lesion SUVpeak/max ≥ 30% reduction) (p < 0.001), with no significant difference in cut-off values between different sites of metastases (i.e., lymph node, bone or visceral metastasis). In patient-level analysis, baseline PSA and SUVpeak values of most avid metastasis were significantly associated with imaging-based response (TL-PSMA ≥ 30% reduction) (p = 0.019 and p = 0.015). In pre-treatment with [68Ga]Ga-PSMA-11 PET/CT, a clear accumulation-response relationship in lesion-level was found for SUVpeak/max in men with mCRPC receiving two cycles of [177Lu]Lu-PSMA-617 treatment. The SUVpeak of the most avid lesion was the only image-derived factor predictive of the imaging-based response at the patient-level.

Hematologic toxicity profile and efficacy of [225Ac]Ac-PSMA-617 α-radioligand therapy of patients with extensive skeletal metastases of castration-resistant prostate cancer

PURPOSE

Actinium-225-labeled prostate-specific membrane antigen ([²²⁵Ac]Ac-PSMA-617) is safe and effective in the treatment of metastatic castration-resistant prostate cancer (mCRPC). No study has specifically assessed its safety in patients with extensive skeletal metastases of mCRPC. We aimed to investigate the hematologic toxicity and efficacy of [²²⁵Ac]Ac-PSMA-617 therapy in patients with extensive skeletal metastases of mCRPC.

METHODS

We retrospectively reviewed the medical record of patients treated with [²²⁵Ac]Ac-PSMA-617 for mCRPC. We included patients with a superscan pattern of skeletal metastases and those with 20 or more multifocal sites of skeletal metastases on baseline [⁶⁸ Ga]Ga-PSMA-11 PET/CT. We reviewed the levels of hemoglobin, white blood cell (WBC), and platelet prior to each cycle of treatment and determined the presence of impaired bone marrow function at baseline and the grade of toxicity in the hematologic parameters induced by treatment. We evaluated the predictors of hematologic toxicity using binary logistic regression analysis. We also determined the presence of renal dysfunction before or during treatment. We assessed response to treatment using prostate-specific antigen response and the progression-free survival (PFS) and overall survival (OS).

RESULTS

A total of 106 patients were included. Skeletal metastasis was in the superscan pattern in 34 patients (32.1%) and multifocal in 72 patients (67.9%). The median treatment cycle was 4 (range = 1-9). Ninety-eight patients (92.5%) had abnormal baseline hematologic parameters. One patient had grade 4 thrombocytopenia. Grade 3 anemia, leukopenia, and thrombocytopenia were seen in 1 (0.9%), 3 (2.8%), and 2 (1.9%) patients, respectively. Age, the number of treatment cycles, and the presence of renal dysfunction were significant predictors of hematologic toxicity. Eighty-five patients (80.2%) achieved PSA response. The median PFS and OS of the study population were 14:00 (95%CI: 8.15-19.86) months and 15.0 (95%CI: 12.8-17.2) months, respectively.

CONCLUSIONS

[²²⁵Ac]Ac-PSMA-617 induces a good anti-tumor effect in about 80% of patients with extensive skeletal metastases of mCRPC with a rare incidence of severe hematologic toxicity. Age, number of treatment cycles, and the presence of renal dysfunction were significant risk factors for hematologic toxicity of [²²⁵Ac]Ac-PSMA-617 therapy.