Safety of PSMA radioligand therapy in mCRPC patients with preexisting moderate to severe thrombocytopenia

Aim of this study was to analyze the safety of prostate-specific membrane antigen radioligand therapy (PSMA-RLT) in patients with metastatic castration-resistant prostate cancer (mCRPC) with preexisting moderate to severe thrombocytopenia (CTCAE ≥ 2).

Seventeen mCRPC patients with preexisting thrombocytopenia (platelet count < 75 × 10⁹/L) were included in this study. Patients received a median of 3 cycles of [¹⁷⁷Lu]Lu-PSMA-617 (range 1–6). The course of platelet cell count was closely monitored within and after the PSMA-RLT and analyzed statistically and according to CTCAE.

No significant difference in platelet counts was observed between baseline and follow-up after each PSMA-RLT cycle: first cycle (54.18 ± 16.07 at baseline vs. 59.65 ± 39.16 at follow up [in × 10⁹/L], p=  0.834), second cycle (58.56 ± 16.43 vs. 107.1 ± 56.44, p = 0.203), and third cycle (60.38 ± 16.57 vs. 132.1 ± 80.43, p = 0.148), respectively. Similarly, baseline and end of treatment values, irrespective of the number of administered cycles, did not reveal a significant difference (54.18 ± 16.07 vs. 72.06 ± 71.9, p = 0.741). After the end of therapy, irrespective of the number of administered cycles, 29.4% of patients remained stable in terms of CTCAE scoring, 41.2% changed to a higher score and 29.4% improved to a lower score. We observed no critical bleeding events due to thrombocytopenia.

Despite the common consideration of marked preexisting thrombocytopenia as a contraindication for RLT, this study indicates feasibility of PSMA-RLT in patients with preexisting thrombocytopenia of grade ≥ 2, as in our preliminary experience, there was no RLT-induced significant deterioration of platelet cell count. Thus, patients with thrombocytopenia should not be categorically excluded from receiving PSMA-RLT.