Purpose: This study aims to evaluate the serum PSA response, Ga-68 PSMA PET/CT response, hematological/nephrological toxicity and survival results of patients with castration-resistant metastatic prostate cancer who are receiving Lu-177 PSMA therapy. Methods: The data of 57 patients with a mean age of 68 years who were treated with Lu-177 PSMA I&T were retrospectively reviewed. Secondary toxicity to treatment was determined using the criteria of the Common Toxicity Criteria for Adverse Events

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... .0. The Kaplan Meier method was used for survival and progression-free survival analysis. Results: Forty percent of patients' serum PSA values' showed >25% regression after the first cycle of treatment. Serum PSA values were stable/ regressed in 75% of the patients. While 2/57 patients showed grade 3 anemia, none showed grade 3 leukopenia or thrombocytopenia. One of 57 patient showed transient nephrotoxicity. Hematological and nephrological toxicity were not observed after treatment of eight cycles, and the serum PSA values of the patients were decreased by 97%. The mean survival time was 11.6 months in all patients, and 17.2 months in patients with serum PSA response. Progression-free survival was an average of 9.9 months. Conclusion: Providing a stable or regressed disease via single cycle treatment in 75% of patients with progression despite the treatments improving survival is an indicator of the success of the therapy. The low rate of hematological and nephrological toxicity in patients (none of the patients that received eight cycles) suggests that the treatment is reliable. Survival was longer in patients with serum PSA response after treatment. Prostate cancer is the second most common type of cancer in males and it accounts for approximately 15% of all cancers worldwide (1). While the 5-year survival rate on localized prostate cancer is 100%, this rate decreases to 31% in the metastatic disease (2). Prostate specific membrane antigen (PSMA) is a glutamate carboxypeptidase II enzyme which is glycoprotein structured and zinc-dependent. There are three parts of this glycoprotein; the intracellular part (19 amino acids), transmembrane part (24 amino acids), and extracellular part (707 amino acids). The enzyme is responsible for folate uptake, cell migration, proliferation, and survival (3). The detection of intensive PSMA expression in prostate cancer has made PSMA a therapeutic target in the treatment of prostate cancer. Prostate cancer cells are sensitive to radiation. Radio-sensitivity is related to high metabolic rate, good nutrient intake, rate of cleavage, and rate of proliferation (4). PSMA expression in prostate cancer is positively associated with tumor stage and early recurrence. In radioligand treatment with Lu-177 PSMA I&T, the radioligand bonds to PSMA from the external side and internalizes into the cell by clathrin-mediated endocytosis (5). This study aims to evaluate the serum PSA response, Ga-68 PSMA PET/CT response, hematological/nephrological toxicity and survival results of patients with castration-resistant metastatic prostate cancer who are receiving Lu-177 PSMA therapy.