Abstract:Objective To investigate the prevalence of Hashimoto’s thyroiditis（HT）in patients with different types of breast cancer，and to provide clinical evidence for thyroid follow-up examinations in breast cancer patients. Methods A total of 370 early - stage breast cancer patients who underwent surgical treatment at Nanjing Drum Tower Hospital from February 2022 to August 2024 were included as the study group. Additionally，192 individuals who underwent health examinations during the same period were included as the control group. Clinical data including age，height，weight，pathology test，and blood test results were collected. Breast cancer was classified into different types based on histopathological results. The diagnosis of HT was based on positive serum thyroglobulin antibodies（TG-Ab）and/or anti-thyroid peroxidase antibodies（TPO -Ab）. Levels of thyroid - stimulating hormone（TSH），free triiodothyronine（FT3），and free thyroxine（FT4）in the blood were analyzed. Results Compared to the control group，the study group had a higher prevalence of HT（28.11% vs 19.79%，χ2=4.630，P<0.05），higher TSH levels［2.47（1.59，3.68）mIU/L vs2.02（1.41，2.82）mIU/L，Z=3.496，P<0.05］，and lower FT4 levels ［16.20（14.72，17.80）pmol/L vs 16.54（15.42，17.88）pmol/L，Z=2.007，P<0.05］. There were differences in the prevalence of HT among different types of breast cancer（χ2=13.078，P<0.05），with triple-negative breast cancer having a higher prevalence of HT compared to Luminal A and breast cancer in situ. In both groups，patients with HT had higher TSH levels than those without HT（P<0.05）. Conclusion Breast cancer patients，especially those with triple-negative breast cancer，have a higher risk of developing HT and hypothyroidism. Therefore，follow-up examinations should include assessments for HT and thyroid function.