Efficacy and Safety of Extended Use of Romiplostim Treatment for Chemotherapy-Induced Thrombocytopenia

Background: Chemotherapy induced thrombocytopenia (CIT) is common, adversely impacts chemotherapy relative dose intensity, and may adversely impact cancer control. There is no approved therapy for CIT. In our recent phase II study of solid tumor patients with CIT (Soff et al, J. Clin. Onc., 2019), romiplostim lead to correction of platelet counts in 85% of participants within 3 weeks. While on romiplostim maintenance, only 6.8% of participants experienced chemotherapy dose reduction or delay as a result of recurrent CIT within a minimum of two cycles of chemotherapy or 8 weeks. However, there is a lack of long-term data on the efficacy and safety of romiplostim in CIT. Objectives: This is an extension analysis of the phase II study for patients receiving romiplostim maintenance for 12 months or longer. Patients/Methods: In the phase II study, 44 patients successfully met the primary endpoint of correction of their platelet count within 3 weeks and resumed chemotherapy with romiplostim maintenance. 21 patients (48%) remained on romiplostim for 12 months or longer. Data were collected from one month prior to initiation of romiplostim to one month after the last dose of drug. Data extracted included complete blood count, chemotherapy doses and dates, romiplostim doses and dates, body weight, cancer diagnosis, age, gender, date of death and thrombotic events. Efficacy was demonstrated by persistent maintenance of platelet counts during long-term chemotherapy and avoidance of episodes of reduced chemotherapy dose intensity. Safety was assessed by two methods: tracking the rates of venous or arterial thrombosis; as well as development of marrow fibrosis and/or secondary hematologic malignancy. The mean romiplostim doses and lab values are calculated by month of study participation. Results: All participants had metastatic disease. Breast (N=6) and colorectal (N=6) were the most common cancers. No participant discontinued romiplostim therapy due to an adverse event or futility. One patient received romiplostim at our institution, but chemotherapy at an outside hospital; details of his chemotherapy were not available for this analysis. 14 of the 20 (70%) of the analyzable participants experienced no episode of CIT; 4 subjects experienced a single chemotherapy dose delay due CIT. No patient experienced multiple delays in chemotherapy due to CIT. Two patients required a chemotherapy dose reduction. The mean monthly platelet counts remained controlled throughout the