RESUMO
OBJECTIVES: Pegfilgrastim is a long-acting, granulocyte colony-stimulating factor approved in Japan for the prevention of neutropenia caused by antineoplastic agents. Severe thrombocytopenia was reported with pegfilgrastim, however, the factors associated with thrombocytopenia are unclear. This study aimed to explore the factors associated with thrombocytopenia in patients with metastatic castration-resistant prostate cancer treated with pegfilgrastim for primary prophylaxis of febrile neutropenia (FN) with cabazitaxel. MATERIALS AND METHODS: This study included metastatic castration-resistant prostate cancer patients who received pegfilgrastim for primary prophylaxis of FN with cabazitaxel. The timing and severity of thrombocytopenia and factors associated with the reduction rate of platelets were examined in patients who received pegfilgrastim for the primary prevention of FN during the first course of cabazitaxel and by multiple regression analysis. RESULTS: Thrombocytopenia was most common within 7 days of pegfilgrastim administration, with 32 cases of grade 1 and 6 cases of grade 2 as per the Common Terminology Criteria for Adverse Events version 5.0. Multiple regression analysis revealed that the reduction rate of platelets after pegfilgrastim administration was significantly positively correlated with monocytes. In contrast, the presence of liver metastases and neutrophils was significantly negatively correlated with the reduction rate of platelets. CONCLUSION: Thrombocytopenia due to pegfilgrastim administered as primary prophylaxis for FN with cabazitaxel was most likely to occur within one week after pegfilgrastim administration, suggesting that monocytes, neutrophils, and liver metastases were associated with a reduction in platelets.