| Summary: | Abstract Background The co-occurrence of breast cancer (BC) and thyroid cancer (TC) has been mentioned for several years, researchers observed an increased risk of BC patients to develop TC, but few researches concern about the features, survival of BC patients followed by TC and the influent factors of the incidence risk. The present study aimed to estimate the clinicopathological features, survival of BC survivors who had primary TC and the predictive factors on the risk of BC patients to develop TC. Methods Women diagnosed with BC between 1992 and 2011, and then developed TC from the Surveillance, Epidemiology, and End Results Database were included. Standardized incidence ratios (SIRs) was used to perform multiple primary analyses, generated from the multiple primary-SIR program in SEER*Stat. Results A total of 842 BC then TC patients were included, the median age was 54 years. Additionally, 78.39% were white, 60.45% had T1 cancer, 62.47% had negative lymph nodes, and more than 75% had infiltrating duct carcinoma, 5-year survival rate was 95.4%. Compared with BC only patients, they were younger, had smaller tumor size and a relatively better prognosis. The risk of developing TC was higher in BC patients than in the general population (SIR 1.22, 95% CI [1.14, 1.31]), especially within 3 years. The influent factors of SIR were black race, BC tumor site, grade and ER/PR positive expression. Conclusions BC patients followed by TC had its particular clinicopathological features. Compared with the features and survival of BC only patients, they were younger, had a smaller tumor size and a relatively better prognosis. Furthermore, BC patients had a high risk of developing TC, especially within 3 years. Black women, primary tumor located in an upper-outer, central, or overlapping site, high grade tumor and with positive hormone receptor expression were predictive factors to develop TC.
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