Breast cancer in thyroid cancer survivors: An analysis of the Surveillance, Epidemiology, and End Results-9 database

BackgroundWe sought to further elucidate the increased risk for breast cancer among survivors of thyroid cancer.MethodsUsing the Surveillance, Epidemiology, and End Results-9 database, we conducted a retrospective cohort analysis on women ≥18 years of age with breast and thyroid cancer from 1973 to 2011.ResultsA total of 707,678 breast cancer patients and 53,853 thyroid cancer patients were included; 1,750 patients developed breast cancer after a preceding diagnosis of thyroid cancer (T1B). Age-specific risk for breast cancer was greater among thyroid cancer survivors. Incidence trends showed a significant age-time interaction and suggested a difference in thyroid cancer biology as well as a treatment effect. Compared with patients with thyroid cancer only, T1B patients were older with smaller cancers, had more follicular thyroid cancers, and fewer patients received radioactive iodine. T1B patients developed breast cancer earlier than the general population, had more estrogen receptor/progesterone receptor-positive and mixed invasive tumor histology, but smaller tumors, and there is no significant difference in the number of lymph nodes involved or radiation therapy.ConclusionThyroid cancer survivors are at greater risk for developing breast cancer than the general population. These patients develop breast cancer early, have more estrogen receptor/progesterone receptor-positive tumors, and have a greater incidence of mixed invasive cancer. Recognition of this association between thyroid and breast cancer should prompt vigilant screening in thyroid cancer survivors and further investigation into the relationship of these 2 diseases.