Chronic myeloid leukaemia following ¹³¹I treatment for thyroid carcinoma: A report of two cases and review of the literature

Leukaemia is an uncommon late complication of exposure to the ionizing radiation of radioactive iodine (¹³¹I). Most cases reported have been of acute leukaemias developing after high doses of ¹³¹I. Only a few cases of chronic myeloid leukaemia (CML) have been reported in this setting to date. We report two new cases of CML after low dose radioactive iodine and review the literature. We present an analysis of the minimal relative risk of CML developing in thyroid cancer patients treated with ¹³¹I in Israel. Two mate patients, 35 and 51 years old, developed CML following low dose ¹³¹I therapy for metastatic mixed papillary and follicular carcinoma of the thyroid. Both had undergone thyroidectomy and neck dissection and thyroid ablation with ¹³¹I (total dose: 56 and 130 mCi respectively). Four and 10 years later, respectively, a leucocytosis was noticed with typical blood smears, and CML was diagnosed either by Philadelphia translocation or bcr-abl gene rearrangement. Thyroid cancer at that time was in remission. Estimated minimal relative risk of CML after ¹³¹I therapy where the population considered at risk comprised all thyroid cancer patients detected during the years 1981-1991 in Israel was 8.95 (95% confidence limits 2.26-35.16). Literature review disclosed five additional similar cases. The mean radioiodine dose given to the seven CML patients was 11416MBq (range 1134-32130MBq), considerably lower than the dose given to patients reported in the literature who subsequently developed acute leukaemias (mean 34965, range 3856-54810 MBq). We suggest that CML is a potential complication of low Ionizing radiation is believed to be leukaemogenic. Both acute leukaemias and chronic myeloid leukaemia (CML) have been reported in atomic bomb survivors and patients treated with X-rays (Ichimaru et al., 1978). Radioactive iodine (¹³¹I) therapy given for thyroid carcinoma can induce leukaemia. Most cases reported in the literature have been of acute leukaemias (Haynie and Beierwaltes, 1963; Brincker et al., 1973; Pochin, 1967; Edmonds and Smith, 1986). CML has been rarely documented after radioiodine therapy for thyroid cancer so the association is less well established. We describe two patients who developed CML several years after low dose radioiodine therapy for thyroid carcinoma and review the relevant literature.