A report published in The Lancet Oncology showed that an analysis of the phase 2 TheraP trial found higher gallium-68–labeled PSMA-11-positron emission tomography (PET) mean standardized uptake values (SUVmean) were associated with a greater likelihood of prostate-specific antigen (PSA) response to lutetium-177–labeled PSMA-617 (LuPSMA) against cabazitaxel in patients with metastatic castration-resistant prostate cancer. Previous reports from the study had shown that LuPSMA improved PSA response rate and progression-free survival compared with cabazitaxel.
The phase 2 TheraP trial included 200 patients randomly assigned to receive LuPSMA 6.0 to 8.5 GBq intravenously every 6 weeks for up to 6 cycles (n=99) or cabazitaxel at 20 mg/m² every 3 weeks for up to 10 cycles. Out of 35 patients in the LuPSMA group and 30 patients in the cabazitaxel group with an SUVmean ≥10 on PSMA PET, PSA response was seen in 32 versus 14 patients. In 64 and 71 patients with an SUVmean <10, response was seen in 33 versus 23 patients.
High-volume disease was seen in 30 patients in both the LuPSMA and cabazitaxel groups, with 69 LuPSMA patients and 71 cabazitaxel patients having a metabolic tumor volume <200 mL. PSA response was seen in 23 of 60 patients in both groups combined, with a metabolic tumor volume ≥200 mL. Response was also seen in 79 of 140 patients with a metabolic tumor volume <200 mL.
The study investigators concluded that “PSMA-PET SUVmean was predictive of higher likelihood of favorable response to LuPSMA than cabazitaxel, which provides guidance for optimal LuPSMA use. High [fluorodeoxyglucose]-PET was associated with lower responses regardless of randomly assigned treatment, warranting further research for treatment intensification. A strength of this analysis is the validation of prespecified cut points within a multicenter, randomized controlled trial. Quantitative PET parameters used, however, require specialized software and are not yet routinely available in most clinics.”
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