title: Randomization to screening for prostate, lung, colorectal and ovarian cancers and thyroid cancer incidence in two large cancer screening trials.
abstract: BACKGROUND
  Thyroid cancer incidence has increased significantly over the past three decades due, in part, to incidental detection. We examined the association between randomization to screening for lung, prostate, colorectal and/or ovarian cancers and thyroid cancer incidence in two large prospective randomized screening trials.
  
  
  METHODS
  We assessed the association between randomization to low-dose helical CT scan versus chest x-ray for lung cancer screening and risk of thyroid cancer in the National Lung Screening Trial (NLST). In the Prostate Lung Colorectal and Ovarian Cancer Screening Trial (PLCO), we assessed the association between randomization to regular screening for said cancers versus usual medical care and thyroid cancer risk. Over a median 6 and 11 years of follow-up in NLST and PLCO, respectively, we identified 60 incident and 234 incident thyroid cancer cases. Cox proportional hazards regression was used to calculate the cause specific hazard ratios (HR) and 95% confidence intervals (CI) for thyroid cancer.
  
  
  RESULTS
  In NLST, randomization to lung CT scan was associated with a non-significant increase in thyroid cancer risk (HR = 1.61; 95% CI: 0.96-2.71). This association was stronger during the first 3 years of follow-up, during which participants were actively screened (HR = 2.19; 95% CI: 1.07-4.47), but not subsequently (HR = 1.08; 95% CI: 0.49-2.37). In PLCO, randomization to cancer screening compared with usual care was associated with a significant decrease in thyroid cancer risk for men (HR = 0.61; 95% CI: 0.49-0.95) but not women (HR = 0.91; 95% CI: 0.66-1.26). Similar results were observed when restricting to papillary thyroid cancer in both NLST and PLCO.
  
  
  CONCLUSIONS
  Our study suggests that certain medical encounters, such as those using low-dose helical CT scan for lung cancer screening, may increase the detection of incidental thyroid cancer.
authors.affiliation: University at Albany, School of Public Health, Rensselaer, New York, United States of America.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: O'Grady
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Rockville, Maryland, United States of America.
authors.forename: Cari M
authors.initials: CM
authors.lastname: Kitahara
authors.affiliation: University at Albany, School of Public Health, Rensselaer, New York, United States of America.
authors.forename: A Gregory
authors.initials: AG
authors.lastname: DiRienzo
authors.affiliation: University at Albany, School of Public Health, Rensselaer, New York, United States of America.
authors.forename: Francis P
authors.initials: FP
authors.lastname: Boscoe
authors.affiliation: University at Albany, School of Public Health, Rensselaer, New York, United States of America.
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Gates
mesh_terms: D000368:Aged; D015179:Colorectal Neoplasms / Q000175:diagnosis*; D055088:Early Detection of Cancer / Q000379:methods; D005260:Female; D006801:Humans; D015994:Incidence; D033162:Incidental Findings; D008175:Lung Neoplasms / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D010051:Ovarian Neoplasms / Q000175:diagnosis*; D011471:Prostatic Neoplasms / Q000175:diagnosis*; D011897:Random Allocation; D013964:Thyroid Neoplasms / Q000453:epidemiology* / Q000209:etiology; D036542:Tomography, Spiral Computed / Q000009:adverse effects / Q000379:methods*