Association of thyroid disorders and breast cancer: A retrospective case-control study

Introduction: This study investigated the association between thyroid disorders and breast cancer. Methods: A retrospective case-control study was conducted using electronic health record data from an academic health care system. This study included 300 female patients 18 years of age and older with a diagnosis of breast cancer and 300 control individuals with no cancer history. Statistical analysis included calculation of prevalence and odds ratios for association, χ² for categorical variables, and mean (SD) and median for age. Results: Patients with breast cancer were, on average, 58 years old, statistically significantly older than patients without cancer (P < .001). Patients were 6 times more likely to have thyroid disorders (P < .001), including hypothyroidism (P < .001), than women who did not have cancer. Patients with triple-negative breast cancer had 4 times higher odds of being diagnosed with thyroid disorders overall (P < .001) and hypothyroidism (P < .001) compared with control individuals. Moreover, patients with estrogen receptor–positive/progesterone receptor–positive breast cancer were 15 times more likely to develop the autoimmune disorder Hashimoto thyroiditis compared with controls, which was statistically significant (P = .026). Discussion: This study highlighted a strong association between breast cancer and thyroid disorders, particularly indicating a higher prevalence of hypothyroidism among individuals with breast cancer.