Iran Medical Council Journal of Iranian Medical Council 2645-338X 9 4 2026 08 01 Changes in Lactobacillus and Bifidobacterium Load in a Population of Iranian People with Papillary Thyroid Cancer: The Effect of Radioactive Iodine therapy 884 890 251594 http://dx.doi.org/10.18502/jimc.v9i4.22456 EN Sakineh Moghadam Shiri Endocrine Research Center, Institute of Endocrinology and Metabolism, Iran University of Medical Science, Tehran, Iran 0000-0002-4460-977X Nahid Hashemi-Madani Endocrine Research Center, Institute of Endocrinology and Metabolism, Iran University of Medical Science, Tehran, Iran 0000-0002-6134-9906 Sara Cheraghi Endocrine Research Center, Institute of Endocrinology and Metabolism, Iran University of Medical Science, Tehran, Iran 0000-0003-2490-2757 Babak Fallahi Research Center for Nuclear Medicine, Dr Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran 0000-0002-0576-1672 Sara Minaeian Antimicrobial Resistance Research Center, Institute of Immunology and Infectious Diseases, Iran University of Medical Sciences, Tehran, Iran 0000-0002-8787-5971 Maryam Honardoost Endocrine Research Center, Institute of Endocrinology and Metabolism, Iran University of Medical Science, Tehran, Iran 0000-0002-1285-8456 Fereshteh Shahrabi Antimicrobial Resistance Research Center, Institute of Immunology and Infectious Diseases, Iran University of Medical Sciences, Tehran, Iran Mohammad E. Khamseh Endocrine Research Center, Institute of Endocrinology and Metabolism, Iran University of Medical Science, Tehran, Iran 0000-0003-4313-8440 Journal Article 2025 05 24 <strong>Background:</strong> To investigate the changes in Lactobacillus and Bifidobacterium load in a population of Iranian people with Papillary Thyroid Carcinoma (PTC) before and following Radioactive Iodine (RAI) therapy.<br><strong>Methods:</strong> This longitudinal cohort study included 28 healthy individuals and 30 PTC patients referred for RAI therapy. A total of 90 stool samples from the same 30 patients with PTC were collected one day before RAI therapy, two weeks and two months following RAI therapy. As a control group, 28 stool samples were collected from 28 healthy age-sex matched individuals. Stool microbiotas were detected using 16S rRNA gene sequencing.<br><strong>Results:</strong> Lactobacillus load was significantly lower in patients with PTC compared to the healthy individuals before (2.56 vs. 4.47 copies/gr stool, p=0.01) and two weeks after RAI therapy (3.51 vs. 4.47 copies/gr stool, p=0.02). Two months after RAI therapy, there was no significant difference in the load of Lactobacillus between the two groups (5.21 vs. 4.47 copies/gr stool, p=0.69). Moreover, the load of Lactobacillus increased significantly from 2.42 copies/gr stool before RAI therapy to 3.80 copies/gr stool at two weeks, and 5.27 copies/gr stool after two months of RAI therapy (p=0.01). On the other hand, there was no difference in the abundance of Bifidobacterium between the PTC and healthy individuals at different time points. <br><strong>Conclusion:</strong> This study indicated the difference in the load of Lactobacillus in PTC patients compared to healthy individuals. Moreover, it highlighted a significant increase in the load of Lactobacillus in PTC patients following RAI therapy. These results highlight the potential for microbiota modulations as an adjuvant therapy in PTC management https://www.jimc.ir/article_251594_9e87c7685d8d56660d7f2be9c10bdd52.pdf