Metformin Attenuates 131I-Induced Decrease in Peripheral Blood Cells in Patients with Differentiated Thyroid Cancer

Background: I-131 treatment (tx) of differentiated thyroid cancer (DTC) is associated with hematopoietic toxicity. It was hypothesized that metformin could have radioprotective effects on bone-marrow function. The objective was to determine whether metformin prevents I-131-induced changes in complete blood counts (CBC) in patients with DTC. Methods: A retrospective analysis was performed of CBC values in DTC patients who were (40 patients: metformin group) or were not taking metformin (39 patients: control group) at the time of administration of I-131. Repeated measures analysis of variance was used for the analysis of the differences in the averages of CBC that were documented at baseline and at 1, 6, and 12 months post I-131 tx. Results: The groups were comparable in terms of age, sex, stage of DTC, I-131 dose administered, and baseline CBC values. In the control group, the decrease in white blood cells (WBC) was 35.8% (p<0.0001) at one month, 21.8% (p<0.0001) at six months, and 19.4% (p<0.0001) at 12 months. In the metformin group, the decrease in WBC was 17.1% (p<0.0001) at one month, and 8.6% at six months (p=0.01), while at 12 months WBC had returned to baseline values (p=0.9). Differences between the two groups were highly statistically significant at all time points (p<0.0001, p=0.0027, and p<0.0001, respectively). Lymphocytes were more sensitive to I-131, but metformin's radioprotective properties were more prominent in neutrophils. At 12 months, the decrease in platelets in the control group was 15.5% (p<0.0001) versus 5.6% (p=0.056) in the metformin group, while at one and six months the reductions in the two groups were comparable. No statistically significant differences were observed between the two groups in the change from baseline values for hemoglobin. Conclusions: Metformin attenuated the I-131-induced decrease in CBC parameters, and its radioprotective properties were more prominent in WBC. Patients who were taking metformin during I-131 tx also experienced a faster recovery in their blood counts, when compared to the control group. Further study is warranted in order to examine if the radioprotective properties of metformin observed in the current study for I-131 tx can also apply to other forms of therapeutic chemo- and radiotherapy.