ABSTRACT
BACKGROUND: Previous studies have reported a strong correlation between breast cancer (BC) and thyroid cancer (TC) incidence. However, the clinical and oncological impact of these associations are not yet fully understood. Here, we aimed to explore the differences in clinicopathological characteristics between TC patients with and without BC, and the effect of a history of positive BC on TC survival. METHODS: We retrospectively compared the clinical characteristics and survival rates of patients with TC alone and those with TC and BC in a primary cohort at our institution and in a second cohort using the Surveillance, Epidemiology, and End Results (SEER) database. RESULTS: In our institutional cohort, survival rates were similar between patients with TC alone and those with TC-associated BC. However, using SEER data, we found that BC had a protective effect on TC patients and was associated with reduced TC mortality rates (hazard ratio [HR] = 0.72, 95% confidence interval [CI] 0.57 to 0.92; P = .026). After stratifying the TC patients according to co-occurring BC subtypes, we observed that higher survival rates were restricted to patients with coexisting luminal A BC (P = .015), which exhibit positive hormone receptors and do not express HER-2. CONCLUSION: These findings suggest that hormone pathways may play a role in the co-occurrence of thyroid and breast cancers. Patients with TC coexisting with luminal A BC have higher survival rates. However, further studies on the mechanisms underlying the association between BC and TC are warranted.
