title: The risk of second cancers after diagnosis of primary thyroid cancer is elevated in thyroid microcarcinomas.
abstract: BACKGROUND
  Thyroid cancers have increased dramatically over the past few decades. Comorbidities may be important, and previous studies have indicated elevated second cancer risk after initial primary thyroid cancers. This study examined the risk of second cancers after development of a thyroid cancer, primary utilizing the Surveillance, Epidemiology, and End Results (SEER) program database.
  
  
  METHODS
  The cohort consisted of men and women diagnosed with first primary thyroid cancer who were reported to a SEER database in 1973-2008 (n=52,103). Standardized incidence ratios (SIR) were calculated for all secondary cancers. Confidence intervals and p-values are at 0.05 significance alpha level and are two-sided based on Poisson exact methods.
  
  
  RESULTS
  In this cohort, 4457 individuals developed second cancers. The risk of developing second cancers after a primary thyroid cancer varied from 10% to 150% depending on different cancer types. Cancers in all sites, breast, skin, prostate, kidney, brain, salivary gland, second thyroid, lymphoma, myeloma, and leukemia were elevated. The magnitude of the risk varied by histology, tumor size, calendar year of first primary thyroid cancer diagnosis, and the treatment of the primary thyroid cancer. The risk of a second cancer was elevated in patients whose first primary thyroid carcinomas were small, or were diagnosed after 1994, or in whom some form of radiation treatment was administered.
  
  
  CONCLUSIONS
  This large population-based analysis of second cancers among thyroid cancer patients suggests that there was an increase of second cancers in all sites, and the most commonly elevated second cancers were the salivary gland and kidney. Additionally, the increase in second cancers in patients with recently diagnosed thyroid microcarcinomas (<10 mm) suggests that aggressive radiation treatment of the first primary thyroid cancer, the environment, and genetic susceptibility, may increase the risk of a second cancer.
authors.affiliation: 1 Yale School of Public Health, Yale University , New Haven, CT 06520, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Kim
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Bi
authors.forename: Dongsheng
authors.initials: D
authors.lastname: Pan
authors.forename: Yingtai
authors.initials: Y
authors.lastname: Chen
authors.forename: Tobias
authors.initials: T
authors.lastname: Carling
authors.forename: Shuangge
authors.initials: S
authors.lastname: Ma
authors.forename: Robert
authors.initials: R
authors.lastname: Udelsman
authors.forename: Yawei
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000473:pathology* / Q000532:radiotherapy / Q000628:therapy; D015331:Cohort Studies; D003131:Combined Modality Therapy; D062665:Epidemiological Monitoring; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D007680:Kidney Neoplasms / Q000453:epidemiology / Q000209:etiology; D008297:Male; D008875:Middle Aged; D016609:Neoplasms, Second Primary / Q000453:epidemiology* / Q000209:etiology; D012042:Registries; D012306:Risk; D012468:Salivary Gland Neoplasms / Q000453:epidemiology / Q000209:etiology; D013964:Thyroid Neoplasms / Q000473:pathology* / Q000532:radiotherapy / Q000628:therapy; D047368:Tumor Burden; D014481:United States / Q000453:epidemiology