Trends in incidence and mortality of "thyroid cancer" in the United States: 2000-2018

Source: Butterfly Academy Over the past few decades, the incidence of thyroid cancer in the United States has increased significantly, which was thought to be mainly due to overdiagnosis of indolent small cancers
.

However, there are also studies suggesting that the incidence of thyroid cancer is actually increasing, as both the incidence of advanced cancer and the incidence-based mortality rate are rising
.

Recent studies have shown a change in thyroid cancer incidence trends after 2013
.

Powers et al reported stable thyroid cancer incidence between 2014 and 2016
.

A follow-up study showed a decrease in the incidence of thyroid cancer between 2015 and 2017
.

However, it is unclear whether the observed reduction in incidence persists
.

Furthermore, it is unclear whether the recently observed downward trend also applies to large or advanced tumors, and whether there is a corresponding change in mortality trends based on morbidity
.

This study aimed to provide updated data on trends in thyroid cancer incidence and mortality in the United States, assess whether incidence trends differed by pathological type and disease extent, and determine whether the observed decline in thyroid cancer incidence led to an incidence-based The mortality rate decreased accordingly
.

The researchers collected data on 197,070 cases of thyroid cancer diagnosed between 2000 and 2018 in the SEER-18 database
.

Most cases were female patients (75.
6%) and white patients (81.
0%)
.

Papillary thyroid carcinoma (PTC) was the most common histological type (89.
1%)
.

The results showed that the overall incidence of thyroid cancer from 2000 to 2018 was 11.
95 cases (95% CI 11.
89 to 12.
00)/100,000 person-years
.

The incidence of thyroid cancer increased from 7.
25 cases (95% CI 7.
06 to 7.
45)/100,000 person-years in 2000 to 14.
53 cases (95% CI 14.
28 to 14.
78)/100,000 person-years in 2014, and then decreased to 2018 13.
48 cases (95%CI 13.
24 to 13.
72)/100,000-years
.

Thyroid Cancer Incidence Trends Thyroid cancer incidence trended upward between 2000 and 2009 (APC 6.
80, 95% CI 6.
46 to 7.
13) and continued to increase between 2009 and 2014, but at a slower rate (APC 2.
58, 95% CI 1.
71 to 3.
47), then declined during 2014-2018 (APC -2.
33, 95% CI -3.
15 to -1.
51) (Fig.
1A)
.

Trends in PTC incidence mirrored general trends in thyroid cancer, which increased during 2000-2009 (APC 7.
44, 95% CI 7.
00 to 7.
88) and continued but at a slower rate during 2009-2014 (APC 3.
14 , 95%CI 2.
01 to 4.
29), and then decreased during 2014-2018 (APC-2.
57, 95%CI-3.
62 to -1.
51) (Fig.
1B)
.

Figure 1.
Thyroid Cancer Incidence and Incidence-Based Mortality Trends: A) Overall Incidence and Mortality Trends, B) Incidence Trends by Pathological Type of Thyroid Cancer Incidence Trends by Stage PTC Incidence Localized Unspread PTC Incidence The rate trend mirrored the overall trend in PTC (Fig.
2A)
.

Incidence of localized unspread PTC increased during 2000-2009 (APC 7.
46, 95%CI 6.
80 to 8.
13) and continued to increase during 2009-2014, but at a slower rate (APC 2.
51, 95%CI 0.
77 to 4.
28), It then decreased during 2014-2018 (APC -3.
51, 95% CI -5.
08 to -1.
91)
.

The incidence of PTC with regional invasion increased between 2000 and 2003 (APC 4.
89, 95% CI 0.
59 to 9.
37), and at a higher rate between 2003 and 2009 (APC 9.
99, 95% CI 8.
44 to 11.
56), 2009 – increased at a slower rate in 2015 (APC 3.
90, 95%CI 2.
71, 5.
10), then declined significantly in 2015–2018 (APC -1.
65, 95%CI -4.
09 to 0.
84)
.

The incidence of PTC with distant metastases remained stable from 2000 to 2015 (APC 0.
47, 95%CI -0.
44 to 1.
39), and then decreased from 2015 to 2018 (APC -17.
86, 95%CI -26.
47 to -8.
25)
.

Trends in the incidence of PTCs of different sizes are shown in Figure 2B, with an increase in the incidence of tumors ≤1.
0 cm between 2000 and 2009 (APC 10.
32, 95% CI 9.
70 to 10.
95), and continued, but at a slower rate, between 2009 and 2014 (APC 2.
66, 95%CI 1.
22 to 4.
11) and then declined during 2014-2018 (APC-5.
83, 95%CI-7.
24 to -4.
40)
.

The incidence of tumors 1.
1-2.
0 cm increased during 2000-2009 (APC 8.
99, 95% CI 8.
34-9.
64) and at a slower rate during 2009-2013 (APC 3.
25, 95% CI 0.
84-5.
71) ), and then remained stable during 2013-2018 (APC-0.
10, 95%CI-1.
16-0.
96)
.

Incidence of tumors of 2.
1-4.
0 cm increased between 2000-2012 (APC 5.
24, 95%CI-4.
72-5.
76) and then non-significantly increased during 2012-2018 (APC 1.
12, 95%CI-0.
17 to 2.
43)
.

The incidence of tumors >4.
0 cm increased during 2000-2014 (APC 5.
77, 95% CI 5.
06 to 6.
48) and then stabilized during 2014-2018 (APC-1.
13, 95% CI-4.
58 to 2.
45)
.

Figure 2.
Trends in incidence of papillary thyroid cancer by disease degree: A) by tumor stage, B) trends in thyroid cancer mortality by tumor size A total of 2,471 people died from thyroid cancer
.

Mortality based on thyroid cancer incidence from 2000 to 2018 was 0.
43 per 100,000 person-years (95% CI 0.
42 to 0.
45)
.

Incidence-based mortality increased from 0.
42 per 100,000 person-years (95% CI 0.
34 to 0.
51) in 2000 to 0.
50 per 100,000 person-years (95% CI 0.
43 to 0.
58) in 2018 (APC 1.
35, 95 %CI 0.
88 to 1.
82), see Figure 1A
.

Mortality was increased for PTC (APC 2.
17, 95% CI 1.
22 to 3.
12) and undifferentiated carcinoma (APC 1.
72, 95% CI 0.
14 to 3.
33), but not for FTC or medullary carcinoma
.

Analysis of PTC mortality stratified by disease severity found increased mortality in PTC with distant metastases (APC 4.
95, 95% CI 3.
06 to 6.
88)
.

Tumors 2.
1–4.
0 cm (APC 3.
65, 95% CI 1.
41 to 5.
93) and >4.
0 cm (APC 4.
29, 95% CI 1.
54 to 7.
12) had increased mortality but not tumors 1.
1–2.
0 cm
.

Tumors ≤1.
0 cm, and APCs with local non-spread and regional invasion could not be counted, as there were 0 deaths within one or more years in these groups
.

   Discussion and Conclusions The increased incidence of thyroid cancer has been attributed solely to overdiagnosis in the past
.

However, there are also studies suggesting that the incidence of thyroid cancer is actually increasing, because the incidence of advanced tumors and the incidence-based mortality rate are rising
.

This study suggests that the improvement of diagnostic ability and the real increase in the incidence of thyroid cancer, the combined effect of the two leads to the above incidence trend
.

From 2014 to 2018, although the total incidence of thyroid cancer and the incidence of small cancers (≤1.
0cm) decreased, the incidence of 2.
1-4.
0cm tumors and ≥4.
0cm tumors remained relatively stable
.

Moreover, thyroid cancer-related mortality continues to increase, especially for thyroid cancer with PTC>2cm and distant metastases
.

These findings suggest that existing thyroid cancer management models may have reduced overdiagnosis of indolent small cancers, but did not affect the incidence of relatively advanced tumors
.

Recent trends in thyroid cancer incidence show a decline in thyroid cancer incidence since 2014
.

Similar declines were seen in PTC, local non-spread, and tumors ≤1.
0 cm
.

These results suggest that the recent decline in incidence may be the result of changes in the management of thyroid nodules
.

In contrast, the increase in mortality based on thyroid cancer incidence suggests that the true increase in incidence cannot be fully explained by overdiagnosis of indolent small cancers
.

Future research is needed to determine the reasons for the current downward trend in thyroid cancer incidence and to monitor future trajectories of thyroid cancer incidence trends to confirm the persistence of the observed downward trend
.