Research Article: Breast cancer prognosis is better in patients who develop subsequent metachronous thyroid cancer

Date Published: May 1, 2019

Publisher: Public Library of Science

Author(s): Kefeng Lei, Xujun He, Leibo Yu, Chao Ni, Hailong Chen, Dandan Guan, Kewang Sun, Hai Zou, Ali S. Alzahrani.


Breast cancer (BC) and thyroid cancer (TC) are common malignancies among females. However, the connection between TC and BC is not well understood. To explore the relationship between these two cancers and to determine the effect of second metachronous TC on BC survival, we compared BC patients with or without second primary TC using data from the Surveillance, Epidemiology, and End Results (SEER) database. We extracted data from patients with only BC or TC and from BC patients with a second metachronous cancer from 2000–2014. Differences in the clinicopathological and treatment characteristics between BC patients with or without second metachronous TC were analyzed by chi-square tests. Multivariate analyses of BC survival were performed by using Cox regression models. Comparison of disease-specific survival (DSS) curves between these cohorts was performed with the log-rank (Mantel-Cox) test. Survival analyses were also performed using data from 1980–1994. Within this dataset, we found 1,262 BC cases in which a second metachronous TC (BC2TC) developed, accounting for 3.1% of all metachronous cancers following BC from 2000–2014. No significant differences were found in molecular markers. In addition, the mean age at BC diagnosis was younger in the BC2TC group than in the BC group (55.418 y vs 60.273 y). Half of the BC2TC patients developed TC in the first three years following BC diagnosis. Patients with BC2TC showed better DSS than those with BC alone from 2000–2014 (P<0.001). However, this superiority was not significant from 1980–1994 (P = 0.579) or for TNM stage I BC (P = 0.927) and grade I BC (P = 0.431) from 2000–2014. In conclusion, the incidence of BC2TC has increased dramatically during the past 15 years. In addition, patients with BC2TC showed better DSS than patients with BC alone, especially in cases from 2000–2014.

Partial Text

Breast cancer (BC) and thyroid cancer (TC) are common malignancies. Although the mortality rate of BC fell between 1989 and 2014, BC remains the second most common cause of cancer-related death among females [1]. In addition, the incidence of TC in the United States has tripled over the past 30 years, with a particularly rapid rise since the 1990s [2].

We used data from the SEER Cancer Registry database, which collects data on every case of cancer reported from 19 U.S. geographical areas. These areas cover approximately 34% of the U.S. population and are representative of the demographics of the entire U.S. population ( We used the following database: Incidence—SEER 18 Regs Custom Data (with additional treatment fields), submitted November 2016 (1973–2014 varying)—Linked to County Attributes—Total U.S., 1969–2015 Counties, National Cancer Institute, DCCPS, Surveillance Research Program, released April 2017. The majority of patients in this study were diagnosed between 1 January 2000 and 31 December 2014. We extracted three cohorts of patients with definite survival months from this database. For cohort one, the total number of in situ/malignant tumors for each patient was 2, with BC as the first malignancy and a second metachronous cancer. In the other cohorts, each patient had only BC or TC. There were 40,520 patients in cohort one, 629,976 patients with only BC and 120,339 patients with only TC. We also extracted cases from 1 January 1980 to 31 December 1994 following the former formula with the second primary TC diagnosed before 1995. All data from SEER database were fully anonymized. The patient records used in our study are provided as supporting databases. The S1 database provides records of the BC cohort from 2000–2014. The S2 database provides records of other cohorts from 2000–2014. The S3 database includes data from all cohorts from 1980–1994.

Is it true that adding TC to primary BC will lead to a worse prognosis than that of BC alone? Our results indicated a better DSS in the BC2TC group than in the BC group, especially for cases between 1 January 2000, and 31 December 2014. In addition, the incidence of TC as a second malignancy following BC has dramatically increased in the last 15 years.