Recent incidences and differential trends of thyroid cancer in the USA

The incidence rate of thyroid cancer has been rising rapidly in recent decades; however, its trend remains unclear. To investigate this, we analyzed the database of the Surveillance, Epidemiology and End Results (SEER) 13, 1992-2012 in the USA, particularly focusing on conventional papillary thyroid cancer (CPTC) and follicular variant of PTC (FVPTC). Of the 75,992 thyroid cancers, 61.3% were CPTC and 25.7% were FVPTC, and their incidence rates (IRs) were significantly increased from 1992 to 2012 (P all < 0.001), with CPTC being 2.4 times of FVPTC (P < 0.001) and the overall average annual percent change (AAPC) of incidence being 6.3% in the former and 5.3% in the latter. IRs were increased in all thyroid cancers, albeit most dramatically in PTC, in virtually all ethnic/demographic groups in recent two decades; however, the incidence trends varied among different thyroid cancers, particularly differentiable between CPTC and FVPTC. For example, Joinpoint analyses revealed that the APC of CPTC before 1996 was 1.5% (P > 0.05), which jumped to 6.8% (P < 0.05) after 1996, whereas the APC of FVPTC before 2000 was 6.6% (P < 0.05), which dropped to 4.8% (P < 0.05) after 2000. IRs and incidence trends of PTC were uneven among different ethnic/demographic groups, as exemplified by the lower IRs of both PTC variants in the Black females than in non-Hispanic White females but higher AAPCs of incidence in the former than in the latter. Interestingly, the data also suggest that the rise in the IRs of PTC is becoming plateaued in the most recent 2 years. These novel observations are helpful in understanding the incidence and incidence trends of thyroid cancer.