Nomograms including [68Gallium (Ga)]Ga-prostate-specific membrane antigen (PSMA)-11 positron emission tomography (PET)/computed tomography (CT) parameters predict outcomes after lutetium-177 (177Lu)-PSMA treatment for patients with metastatic castration-resistant prostate cancer (mCRPC), according to a study published online July 8 in The Lancet Oncology.
Andrei Gafita, M.D., from the University of Duisburg-Essen in Germany, and colleagues screened patients with mCRPC who had received 177Lu-PSMA between Dec. 10, 2014, and July 19, 2019. Eligible patients had a baseline [68Ga]Ga-PSMA-11 PET/CT scan and received 6.0 to 8.5 GBq 177Lu-PSMA once every six to eight weeks for a maximum of four to six cycles. A total of 270 patients were eligible and were divided into development and validation cohorts (196 and 74 participants, respectively). Nomograms for overall survival and prostate-specific antigen (PSA) progression-free survival were computed.
Patients were followed for a median of 21.5 months. Time since initial diagnosis of prostate cancer, chemotherapy status, baseline hemoglobin concentration, and [68Ga]Ga-PSMA-11 PET/CT parameters were included as predictors in the nomograms. The researchers found that the C-index was 0.71 for the overall survival model and 0.70 for the PSA progression-free survival model. For both outcomes, similar C-indices were achieved at internal and external validation. Both models were adequately calibrated, and there was a correlation observed for their predictions with the observed outcome.
“Our findings validate PSMA-PET companion imaging as a gatekeeper for patient selection and as a quantitative prognostic biomarker,” the authors write. “Our nomograms, integrated in an online risk calculator, can assist in clinical trial design and individual clinical decision making.”
Several authors disclosed financial ties to the biopharmaceutical industry; one author holds a patent application for rhPSMA.