Clinical Variables Associated with PSA Response to Lutetium-177-PSMA ([177Lu]-PSMA-617) Radionuclide Treatment in Men with Metastatic Castration-Resistant Prostate Cancer.

Lutetium-177-PSMA ([177Lu]-PSMA-617), a radiolabeled small molecule, binds with high affinity to prostate-specific membrane antigen (PSMA), enabling targeted radiation therapy to metastatic prostate lesions. Our objective was to retrospectively analyze the activity of [177Lu]-PSMA-617 given off-trial to men with metastatic castration resistant prostate cancer (mCRPC) and identify clinical factors associated with PSA response. Electronic medical records of all men treated with [177Lu]-PSMA-617 were reviewed and analyzed. Overall survival was calculated using the Kaplan-Meier method. The association between potential variables and PSA response was analyzed by univariate analysis, using either logistic regression or χ2/Fisher's exact test. Multivariable analysis was carried out using logistic regression on all categorical variables with a P-value of <0.1 on univariate analysis. Variables found to be statistically significant were then used to define a categorical score. A total of 52 patients received at least one cycle of [177Lu]-PSMA-617. Clinical benefit was observed in 28 patients (52%). PSA decline ≥20% and ≥50% was observed in 26 (50%) and 18 patients (35%), respectively. Achievement of any PSA decline at first measurement was significantly associated with survival. There was a negative association between the number of previous chemotherapy lines and PSA decline above 20%. Univariate analysis followed by multivariable analysis showed that older age and higher hemoglobin were significantly associated with a PSA decline >20%. A score combining these two parameters was significantly associated with PSA response. In summary, [177Lu]-PSMA-617 is active in the 'real-life' setting of heavily pretreated men with mCRPC.