title: Simultaneous medullary and differentiated thyroid cancer: a population-level analysis of an increasingly common entity.
abstract: BACKGROUND
  Simultaneous medullary thyroid carcinoma (MTC) and differentiated thyroid carcinoma (DTC) is a rare entity. This is the first population-level analysis of the characteristics and outcomes of simultaneous MTC/DTC.
  
  
  METHODS
  In the Surveillance, Epidemiology, and End Results (SEER) database (1988-2008), patients with simultaneous MTC/DTC were retrospectively compared with those with MTC alone using χ(2), ANOVA, log-rank tests, Cox multivariate regression, and Kaplan-Meier analyses.
  
  
  RESULTS
  A total of 162 patients had simultaneous MTC/DTC; 1,699 had MTC alone. MTC was diagnosed first in 67.9 % of simultaneous MTC/DTC cases. Simultaneous MTC/DTC increased from 2.7 % of all MTCs in 1988-1997 to 12.3 % in 2003-2008. Compared with MTC alone, simultaneous MTC/DTC had smaller mean MTC tumor size (2.9 vs. 2.2 cm; p = 0.005) and lower rates of MTC extrathyroidal extension (25.4 vs. 16.8 %; p = 0.015) and distant metastases (15.7 vs. 9.3 %; p = 0.032). Patients diagnosed with DTC first had smaller mean MTC tumor sizes (p = 0.01), whereas patients diagnosed with MTC first had tumor sizes similar to those of MTC alone. Compared with MTC alone, patients with simultaneous MTC/DTC were more likely to receive thyroidectomy (84.7 vs. 93.2 %; p = 0.003) and radioisotopes (4.4 vs. 25 %; p < 0.001). On Kaplan-Meier analysis, disease-specific survival rates were higher for simultaneous MTC/DTC than for MTC alone (10-year survival rates 87 vs. 81 %; p = 0.056).
  
  
  CONCLUSIONS
  Simultaneous MTC/DTC is diagnosed earlier in tumor development than MTC alone, with a trend toward better prognosis. This entity likely represents a primary tumor with an incidental pathologic finding of a second malignancy. Each malignancy should be treated according to its respective stage and current guidelines.
authors.affiliation: Department of Surgery, Yale University School of Medicine, New Haven, CT, USA.
authors.forename: Risa L
authors.initials: RL
authors.lastname: Wong
authors.forename: Hadiza S
authors.initials: HS
authors.lastname: Kazaure
authors.forename: Sanziana A
authors.initials: SA
authors.lastname: Roman
authors.forename: Julie A
authors.initials: JA
authors.lastname: Sosa
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018276:Carcinoma, Medullary / Q000175:diagnosis* / Q000453:epidemiology / Q000401:mortality; D003237:Connecticut / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009378:Neoplasms, Multiple Primary / Q000175:diagnosis* / Q000453:epidemiology / Q000401:mortality; D011379:Prognosis; D012189:Retrospective Studies; D018426:SEER Program; D015996:Survival Rate; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000453:epidemiology / Q000401:mortality; D055815:Young Adult