Bone Marrow Function After I-131 Therapy in Patients With Differentiated Thyroid Carcinoma

Objective: The primary objective was to evaluate the short-and long-term toxic effects of radioiodine (I-131) therapy on bone marrow function in differentiated thyroid carcinoma (DTC) patients. The secondary objective was to define characteristics of patients at risk for impaired bone marrow function after I-131 treatment.Patients and Methods: DTC patients treated with I-131 between 1989 and 2013 were included. We excluded patients with morbidities or treatments that could have influenced blood count parameters. Baseline platelets, leukocytes, and hemoglobin levels were compared with blood counts at 3 and 6 months and at 1 and 5 years after treatment. Logistic multivariate regression analyses were performed to determine patient characteristics associated with thrombocytopenia.Results: We included 331 patients. Mean +/- SD age was 47.5 +/- 17.2 years, and 74.0% were female. Posttreatment platelets were significantly decreased at 6 months and 1 year, as compared with baseline. Leukocyte counts were also decreased at 3 and 6 months and at 1 year after treatment. No decreases in hemoglobin were found. Five years after treatment, platelet and leukocyte counts were comparable with baseline. Fourteen patients (4.2%) developed transient posttreatment thrombocytopenia. Risk factors for thrombocytopenia were older age, T4 tumor stage, male gender, and cumulative dose 131I. After a multivariate regression analysis, the cumulative dose 131I remained independently associated with thrombocytopenia.Conclusion: Posttreatment platelets and leukocytes were transiently decreased compared with pretreatment values in a general DTC population. Cumulative I-131 dose was independently associated with thrombocytopenia. Platelets and leukocytes normalized to baseline levels 5 years after treatment, implying that in most patients the clinical effects of bone marrow toxicity are limited.