Thyrotropin suppression therapy using levothyroxine does not negatively affect breast cancer prognosis

Breast cancer (BC) and thyroid dysfunction are common in females, yet the relationship between thyroid hormone and BC is unclear. To search for the connection between thyrotropin and BC, we contradistinguished BC patients with or without synchronous second primary thyroid cancer (TC) with surgery using data from the Surveillance, Epidemiology, and End Results (SEER) database. Theoretically, according to the ATA (American Thyroid Association) guidelines, all TC patients were treated with thyrotropin suppressive therapy only from 2010 to 2015.

Data from BC patients with a synchronous second TC with surgery (BC2TC) and only BC patients (1BC) during 2010-2015 were extracted from the SEER database. Differences in the clinicopathological characteristics between BC2TC and 1BC patients were analyzed by chi-square tests. Comparisons of the disease-specific survival (DSS) and overall survival (OS) curves between these two groups were performed with the log-rank (Mantel-Cox) test.

Within this dataset, we identified 134 BC2TC patients during the period from 2010 to 2015. Significant differences between the BC2TC and 1BC groups were found only for different ages and TNM (tumor-node-metastasis status) stages. There were no significant differences in DSS between the two cohorts (P = 0.060). The same tendencies in OS or DSS were observed for the different age groups and different TNM groups, even the stage I, N0 (without metastases to lymph nodes), and ER (+) (estrogen receptor (ER)-positive) groups.

There were no remarkable differences in survival between the BC2TC and 1BC groups, and thyrotropin suppression therapy using levothyroxine did not negatively affect BC prognosis.