Chapter 4: Cancer incidence in Canada: trends and projections (1983-2032) – Thyroid cancer - HPCDP: Volume 35, Supplement 1, Spring 2015

Chapter 4: Projections by Cancer Site

19. Thyroid cancer

The average annual number of thyroid cancer in 2003–2007 was 795 in males and 2810 in females, representing 1.0% and 3.8% of all new Canadian male and female cancer cases, respectively (Tables 4.19.1 and 4.19.2).

TABLE 4.19.1
Observed (2003–2007) and projected average annual new cases by age and province/territories combined (TC), cancer of thyroid, males, Canada, 2003–2032
Period Age New cases
CA BC AB SK MB ON QC NB NS PE NL TC

Abbreviations: AB, Alberta; BC, British Columbia; CA, Canada; MB, Manitoba; NB, New Brunswick; NL, Newfoundland and Labrador; NS, Nova Scotia; ON, Ontario; PE, Prince Edward Island; QC, Quebec; SK, Saskatchewan; TC, All Territories (Yukon, Northwest Territories and Nunavut).

Note: Totals may not add up due to rounding.

2003–07 <45 255 20 25 5 5 130 50 5 5 0 0 0
45–54 190 15 20 5 5 95 40 5 5 0 5 0
55–64 175 15 15 5 5 80 45 5 5 0 5 0
65–74 115 10 10 0 5 50 25 5 5 0 0 0
75–84 50 5 5 0 0 20 10 0 5 0 0 0
85+ 5 0 0 0 0 5 0 0 0 0 0 0
Total 795 60 75 15 20 380 180 20 25 5 10 0
2008–12 <45 295 20 30 5 5 150 60 5 5 0 0 0
45–54 245 15 25 5 5 125 50 5 5 0 5 0
55–64 240 15 25 5 5 120 60 5 5 0 5 0
65–74 170 15 15 5 5 80 45 5 5 0 5 0
75–84 75 5 5 0 0 30 20 0 0 0 0 0
85+ 15 0 0 0 0 10 5 0 0 0 0 0
Total 1035 75 100 15 20 515 240 30 30 5 15 0
2013–17 <45 320 20 25 5 5 175 70 10 5 0 0 0
45–54 275 15 30 5 5 145 60 5 5 0 5 0
55–64 320 20 30 5 5 170 75 10 10 0 5 0
65–74 255 15 20 5 5 125 65 10 10 0 5 0
75–84 95 10 10 0 0 40 25 5 5 0 0 0
85+ 20 0 0 0 0 10 5 0 0 0 0 0
Total 1290 85 120 15 25 665 300 35 35 5 15 0
2018–22 <45 335 25 25 5 5 190 70 10 10 0 0 0
45–54 290 20 30 5 5 145 70 10 5 0 0 0
55–64 395 20 40 5 5 210 95 5 10 0 5 0
65–74 340 20 35 5 5 175 85 10 10 0 5 0
75–84 135 10 15 0 0 60 40 5 5 0 0 0
85+ 30 0 0 0 0 15 5 0 0 0 0 0
Total 1525 95 145 15 25 800 365 40 40 5 15 0
2023–27 <45 325 25 25 5 10 190 65 10 10 0 0 0
45–54 305 15 25 5 5 160 75 10 5 0 0 0
55–64 420 20 50 5 5 220 105 5 10 0 5 0
65–74 425 20 45 5 5 230 105 10 15 0 5 0
75–84 195 15 20 0 0 90 60 5 5 0 5 0
85+ 40 0 5 0 0 20 10 0 0 0 0 0
Total 1710 100 170 15 25 905 425 40 45 5 10 0
2028–32 <45 330 25 25 5 10 205 65 15 10 0 0 0
45–54 310 15 25 5 5 160 75 10 5 0 0 0
55–64 425 20 45 5 5 215 115 5 10 0 0 0
65–74 510 25 55 5 5 275 135 5 15 0 5 0
75–84 255 15 30 0 0 125 75 5 5 0 0 0
85+ 60 5 5 0 0 35 15 0 0 0 0 0
Total 1895 105 190 20 25 1010 485 45 50 5 10 0
TABLE 4.19.2
Observed (2003–2007) and projected average annual new cases by age and province/territories combined (TC), cancer of thyroid, females, Canada, 2003–2032
Period Age New cases
CA BC AB SK MB ON QC NB NS PE NL TC

Abbreviations: AB, Alberta; BC, British Columbia; CA, Canada; MB, Manitoba; NB, New Brunswick; NL, Newfoundland and Labrador; NS, Nova Scotia; ON, Ontario; PE, Prince Edward Island; QC, Quebec; SK, Saskatchewan; TC, All Territories (Yukon, Northwest Territories and Nunavut).

Note: Totals may not add up due to rounding.

2003–07 <45 1225 80 125 15 30 670 240 30 25 0 10 0
45–54 695 45 65 10 15 360 155 20 15 0 10 0
55–64 470 30 35 10 10 240 110 15 10 0 10 0
65–74 250 15 20 5 5 125 70 5 5 0 5 0
75–84 130 15 10 5 5 55 35 5 5 0 5 0
85+ 35 5 5 0 0 10 10 0 0 0 0 0
Total 2810 185 260 45 60 1460 615 75 65 5 35 5
2008–12 <45 1440 90 150 20 30 785 285 35 35 0 15 5
45–54 985 55 90 10 20 550 210 35 20 0 10 0
55–64 755 40 60 10 15 410 175 20 15 0 15 0
65–74 385 20 30 5 5 195 100 10 10 0 5 0
75–84 180 15 10 5 5 80 50 10 5 0 5 0
85+ 55 5 5 0 0 20 15 0 0 0 0 0
Total 3805 230 345 50 75 2045 830 110 85 5 50 5
2013–17 <45 1570 100 155 20 40 860 310 45 40 0 15 5
45–54 1230 65 110 10 20 725 245 40 20 0 10 0
55–64 1065 55 85 10 15 600 250 25 20 0 15 0
65–74 610 30 45 5 10 325 155 20 15 0 10 0
75–84 245 15 15 5 5 115 65 10 5 0 5 0
85+ 75 5 10 0 0 30 20 5 0 0 0 0
Total 4800 270 420 55 90 2655 1045 150 105 5 60 5
2018–22 <45 1620 100 155 20 40 900 320 50 40 5 20 5
45–54 1320 70 120 10 20 780 260 50 20 0 15 0
55–64 1385 65 110 15 20 815 315 40 25 0 15 0
65–74 895 45 65 10 15 500 225 25 20 0 10 0
75–84 345 20 25 5 5 170 90 20 10 0 5 0
85+ 100 5 10 0 0 45 30 5 0 0 0 0
Total 5670 300 485 60 100 3205 1240 185 115 5 65 10
2023–27 <45 1570 90 145 20 45 890 295 55 45 5 20 5
45–54 1355 75 120 10 25 780 280 55 20 0 15 0
55–64 1580 70 125 10 20 970 340 45 20 0 15 0
65–74 1165 50 90 10 15 660 290 35 20 0 10 0
75–84 510 25 30 5 10 260 135 25 10 0 10 0
85+ 135 5 15 0 0 60 40 5 5 0 0 0
Total 6315 325 530 65 115 3620 1385 215 120 10 70 10
2028–32 <45 1520 80 130 20 45 875 290 55 50 5 20 5
45–54 1395 85 130 10 30 800 285 60 20 0 15 0
55–64 1630 75 130 10 20 1000 345 50 20 0 15 0
65–74 1455 60 110 10 15 860 360 45 20 0 10 0
75–84 725 40 45 10 10 385 185 30 15 0 10 0
85+ 185 10 20 5 5 85 55 10 5 0 0 0
Total 6910 345 565 65 125 4005 1515 250 125 10 70 10

Whereas incidence rates for all cancers combined and for most specific types of cancer in Canada are stable or decreasing, thyroid cancer rates are rising significantly in both sexes. Though relatively uncommon in Canada, thyroid cancer is the most rapidly increasing of all cancers in both sexes. This increase has been particularly rapid in females over the past 25 years, such that thyroid cancer was the sixth most common cancer in females in Canada during the last observation period (2003–2007) (Table 4.19.3 and 4.19.4).

TABLE 4.19.3
Observed (2003–2007) and projected age-standardized incidence rates (ASIRs) by age and province/territories combined (TC), cancer of thyroid, males, Canada, 2003–2032
Period Age ASIRs
CA BC AB SK MB ON QC NB NS PE NL TC

Abbreviations: AB, Alberta; BC, British Columbia; CA, Canada; MB, Manitoba; NB, New Brunswick; NL, Newfoundland and Labrador; NS, Nova Scotia; ON, Ontario; PE, Prince Edward Island; QC, Quebec; SK, Saskatchewan; TC, All Territories (Yukon, Northwest Territories and Nunavut).

2003–07 <45 2.5 1.4 2.3 1.4 1.8 3.3 2.2 2.1 2.1 5.5 1.2 2.1
45–54 7.7 4.3 7.0 4.6 4.9 10.2 6.8 10.7 7.7 6.4 6.4 0.0
55–64 10.0 5.4 9.6 6.5 7.0 12.0 10.4 10.9 9.6 4.9 11.4 5.5
65–74 10.9 7.2 12.6 6.3 7.1 12.5 10.3 17.4 12.3 24.1 8.5 0.0
75–84 8.5 6.0 11.8 5.3 7.4 8.9 8.6 9.7 14.1 0.0 4.2 0.0
85+ 4.3 3.3 4.6 5.3 2.8 5.3 3.8 4.9 3.7 0.0 0.0 0.0
Total 4.5 2.6 4.5 2.7 3.1 5.7 4.2 5.1 4.5 6.6 3.2 1.9
2008–12 <45 3.0 1.5 2.3 1.6 1.6 3.9 2.7 3.1 2.7 2.5 0.7 1.2
45–54 9.0 4.5 8.3 4.3 4.4 12.1 8.0 10.0 8.6 8.0 7.0 3.7
55–64 11.5 5.3 11.7 5.4 8.1 15.3 11.4 13.3 10.9 11.4 12.2 4.8
65–74 13.8 7.5 13.5 7.1 8.5 16.9 13.7 22.7 16.6 14.2 15.8 5.7
75–84 10.6 7.0 12.8 5.5 5.7 12.0 11.7 13.9 11.9 10.5 6.0 4.4
85+ 7.4 3.9 6.3 5.2 4.0 10.3 6.3 9.0 9.0 8.3 18.1 3.1
Total 5.4 2.8 4.9 2.8 3.1 7.0 5.2 6.5 5.4 5.0 3.7 2.2
2013–17 <45 3.1 1.6 2.1 1.6 1.8 4.3 3.0 4.0 3.1 2.9 0.8 1.3
45–54 10.4 4.6 10.3 4.3 3.8 13.5 10.0 11.6 9.8 9.1 6.3 4.3
55–64 13.4 5.7 12.3 5.7 8.3 18.8 13.0 14.0 12.4 13.0 9.0 5.6
65–74 16.3 7.6 15.7 6.2 7.9 21.3 16.9 23.8 18.7 16.1 18.8 6.8
75–84 12.4 7.6 14.8 5.5 6.5 13.9 14.2 19.5 13.4 12.0 10.2 5.2
85+ 7.8 3.2 7.4 3.8 3.7 10.6 8.1 8.7 10.2 9.3 8.6 3.2
Total 6.1 2.9 5.3 2.7 3.2 8.1 6.0 7.7 6.1 5.7 3.8 2.5
2018–22 <45 3.1 1.6 2.0 1.6 1.9 4.5 2.8 4.9 3.4 3.1 0.9 1.3
45–54 11.6 5.1 10.0 4.2 4.7 14.7 12.5 15.4 10.7 10.0 2.6 4.8
55–64 15.1 5.8 14.6 5.6 6.1 20.6 15.5 10.4 13.5 14.2 9.0 6.3
65–74 18.0 6.9 18.8 5.1 6.9 24.7 19.1 23.4 20.2 17.6 15.4 7.5
75–84 14.8 8.0 15.8 6.2 5.8 17.5 17.1 23.7 14.6 13.1 13.0 6.2
85+ 9.7 4.4 8.3 4.5 4.1 13.5 10.3 7.8 11.2 10.3 6.6 4.0
Total 6.6 2.9 5.7 2.7 3.1 8.9 6.7 8.4 6.7 6.2 3.3 2.7
2023–27 <45 3.0 1.6 2.0 1.6 2.0 4.3 2.8 5.3 3.5 3.3 1.0 1.2
45–54 12.2 4.8 8.8 4.2 5.2 16.1 13.6 17.3 11.2 10.5 2.9 5.1
55–64 16.3 5.7 17.8 5.6 4.4 21.2 18.3 9.5 14.1 14.8 8.0 6.8
65–74 19.6 7.3 19.5 5.6 5.8 27.5 20.9 19.6 20.9 18.3 9.6 8.2
75–84 16.3 7.8 18.6 4.6 4.3 19.9 20.2 19.4 15.2 13.7 12.6 6.8
85+ 10.3 4.1 10.0 4.2 3.7 13.4 11.8 10.4 11.7 10.7 10.5 4.3
Total 6.8 2.9 6.0 2.6 2.9 9.3 7.2 8.5 7.0 6.5 2.9 2.8
2028–32 <45 3.0 1.6 2.0 1.6 2.1 4.6 2.8 5.9 3.7 3.4 1.1 1.2
45–54 11.5 4.5 8.3 4.2 5.8 14.9 12.3 19.3 11.7 11.0 3.3 4.8
55–64 17.6 6.2 17.4 5.6 4.9 21.9 21.9 11.4 14.7 15.6 2.6 7.3
65–74 21.2 7.0 23.1 5.6 3.8 28.8 24.4 13.2 21.7 19.3 10.6 8.8
75–84 17.5 6.9 21.8 4.4 3.3 22.4 22.3 17.7 15.8 14.4 8.3 7.3
85+ 12.5 4.5 10.0 5.1 2.7 17.8 14.5 10.8 12.2 11.2 11.8 5.2
Total 7.0 2.9 6.3 2.6 2.9 9.6 7.8 8.8 7.3 6.8 2.5 2.9
TABLE 4.19.4
Observed (2003–2007) and projected age-standardized incidence rates (ASIRs) by age and province/territories combined (TC), cancer of thyroid, females, Canada, 2003–2032
Period Age ASIRs
CA BC AB SK MB ON QC NB NS PE NL TC

Abbreviations: AB, Alberta; BC, British Columbia; CA, Canada; MB, Manitoba; NB, New Brunswick; NL, Newfoundland and Labrador; NS, Nova Scotia; ON, Ontario; PE, Prince Edward Island; QC, Quebec; SK, Saskatchewan; TC, All Territories (Yukon, Northwest Territories and Nunavut).

2003–07 <45 12.6 6.6 11.9 5.9 8.3 17.1 10.8 13.2 9.2 6.0 6.8 5.8
45–54 28.1 13.6 26.5 13.7 15.5 38.8 25.2 31.1 21.2 13.7 20.9 20.0
55–64 26.2 12.2 23.7 16.9 16.6 35.7 23.6 31.7 18.2 7.6 26.0 33.0
65–74 21.5 8.2 22.5 12.2 9.3 27.1 22.7 23.1 20.2 7.3 20.6 0.0
75–84 15.2 11.6 12.2 14.4 12.9 16.1 15.5 22.8 20.3 6.0 23.1 0.0
85+ 9.9 5.8 17.5 7.7 8.7 8.1 12.1 10.5 12.8 21.4 15.7 0.0
Total 16.1 8.1 15.3 8.5 10.0 21.6 14.4 17.7 12.4 7.2 11.6 9.0
2008–12 <45 14.7 7.1 13.3 6.8 9.5 20.0 13.1 17.8 12.9 5.9 9.7 8.1
45–54 36.9 15.5 31.9 14.6 19.7 53.2 32.8 52.4 23.4 10.8 24.9 20.2
55–64 34.9 14.0 29.9 15.7 18.1 50.8 32.5 34.5 24.8 8.6 32.0 19.1
65–74 28.6 11.1 28.4 12.8 12.6 37.9 28.9 37.0 25.2 8.6 28.5 15.6
75–84 20.2 12.2 15.3 15.4 13.0 23.4 21.2 36.8 19.2 9.3 26.7 11.1
85+ 13.0 6.6 19.6 10.3 10.3 12.6 16.2 16.5 13.3 10.5 11.9 7.1
Total 20.0 9.1 17.9 9.1 11.7 27.5 18.3 24.9 16.1 7.0 15.2 10.9
2013–17 <45 15.6 7.1 13.1 7.2 10.7 21.3 14.0 22.2 15.1 6.3 12.4 8.5
45–54 47.2 18.1 40.7 15.5 22.0 69.0 42.0 71.4 27.4 12.0 30.4 25.8
55–64 43.5 15.7 35.9 16.6 19.0 64.7 41.9 45.1 29.9 9.8 33.9 23.8
65–74 36.1 12.8 30.8 13.5 16.3 50.8 36.9 49.2 26.8 9.7 34.0 19.8
75–84 26.0 12.3 21.5 16.3 13.1 31.7 27.0 45.9 24.8 10.6 32.7 14.2
85+ 15.2 8.4 18.8 10.9 11.5 15.2 17.8 24.5 14.3 12.0 19.0 8.3
Total 23.1 9.6 19.6 9.7 13.1 32.5 21.5 32.2 18.9 7.6 18.4 12.7
2018–22 <45 15.3 6.7 12.5 7.5 11.4 21.1 13.9 24.6 16.6 6.5 14.5 8.4
45–54 53.5 20.0 44.2 16.1 24.6 77.3 49.5 91.9 33.1 13.0 37.5 29.3
55–64 52.3 17.0 41.0 17.2 21.6 78.6 51.5 64.8 29.2 11.0 34.5 28.6
65–74 44.1 14.8 35.8 14.1 18.6 64.7 45.2 49.6 29.2 11.0 31.6 24.1
75–84 31.1 12.5 24.3 16.9 14.6 39.5 32.3 65.0 27.2 12.2 37.4 17.0
85+ 18.0 8.4 19.0 11.4 9.3 20.0 21.9 32.4 11.4 13.8 14.7 9.8
Total 25.1 9.8 20.5 10.0 14.2 35.7 23.8 38.5 20.6 8.2 20.7 13.8
2023–27 <45 14.3 5.9 11.3 7.6 11.4 19.8 12.8 25.9 18.0 6.8 15.8 7.8
45–54 54.0 21.3 43.1 16.4 29.7 76.6 52.1 107.4 30.4 13.8 41.9 29.6
55–64 61.1 18.9 48.5 17.5 23.3 92.4 60.1 78.1 28.9 12.2 32.8 33.4
65–74 50.2 15.6 40.0 14.3 18.6 74.5 53.5 58.0 29.4 12.5 27.5 27.4
75–84 36.2 13.7 24.8 17.2 18.1 48.3 38.1 72.8 24.3 13.8 35.4 19.8
85+ 21.8 7.9 27.3 11.6 9.9 24.7 25.7 34.2 15.5 15.9 17.9 11.9
Total 25.9 9.6 20.5 10.2 15.1 37.0 24.9 43.1 21.2 8.7 21.6 14.2
2028–32 <45 13.7 5.2 10.2 7.7 11.6 18.9 12.5 27.2 19.5 7.0 17.1 7.5
45–54 51.9 21.7 42.8 16.7 30.9 74.1 48.9 112.9 28.2 14.3 46.7 28.4
55–64 66.6 20.4 51.2 17.9 25.0 99.5 67.8 95.5 31.8 13.3 36.0 36.5
65–74 57.9 16.6 44.2 14.6 21.0 86.8 62.7 77.6 26.1 14.1 24.3 31.7
75–84 42.4 15.4 28.6 17.5 19.6 58.9 44.8 69.0 24.5 15.6 29.4 23.2
85+ 24.5 8.1 26.6 11.9 10.9 29.2 29.3 52.1 13.2 18.2 16.6 13.4
Total 26.5 9.5 20.4 10.4 15.8 37.9 25.9 47.5 22.0 9.2 22.9 14.5

Over the entire observation period, Ontario experienced the fastest growth in rates, British Columbia had the slowest linear increase, and other regions had similar moderate increases in between (Figure 4.19.1).

FIGURE 4.19.1
Age-standardized incidence rates (ASIRs) by region, thyroid cancer, 1983–2032

Age-standardized incidence rates (ASIRs) by region, thyroid cancer, 1983–2032

[Click to enlarge]

[FIGURE 4.19.1, Text Equivalent]

Health Promotion and Chronic Disease Prevention in Canada - Volume 35 · Supplement 1 · Spring 2015

FIGURE 4.19.1
Age-standardized incidence rates (ASIRs) by region, thyroid cancer, 1983-2032

Over the entire observation period, thyroid cancer rates were rising significantly in both sexes. The rates are projected to increase in all regions, with the most prominent increase in Ontario and the least evident one in British Columbia. Internal ranking of ASIRs according to region is projected to be similar for males and females, with the highest rates in Ontario and the lowest in British Columbia. It is useful to acknowledge that forecasting thyroid cancer incidence is subject to some uncertainty as a result of recent large increase in the rates likely because of increased diagnostic scrutiny.

One in 223 males and 1 in 71 females can expect to be diagnosed with thyroid cancer in their lifetime, and 1 in 1937 males and 1 in 1374 females can expect to die from it.Endnote 36 Thyroid cancer has the highest 5-year relative survival rate of all cancers in Canada, at 98% in 2006–2008.Endnote 1

Joinpoint analysis (data not shown, but the similar annual percent changes for males and the annual percent changes for females in their respective most recent observation periods are shown in Figure 3.1 or 3.2) further showed that the ASIRs of thyroid cancer in males in Canada increased 2.7% per year from 1986 to 1997 and then rose more quickly at 6.7% per year through 2007. The rates for females increased 4.4% per year during 1986 through 1998, accelerated to an 11.4% annual increase from 1998 to 2002 and thereafter rose more slowly by 6.9% annually. Cases are generally diagnosed at younger ages relative to other cancers. In 2003–2007, approximately 44% of new thyroid cancer cases in females were diagnosed in those aged under 45, 25% in those aged 45 to 54, 17% in those aged 55 to 64 and 15% in those aged 65 or older. For males, the corresponding percentages for the same age groups were 32%, 24%, 22% and 21% (Tables 4.19.1 and 4.19.2).

Through the entire observation period, the ASIRs were higher in females than in males in all age groups. The female-to-male ratio was highest in the youngest age group (<45), decreased steadily with age up to age 74 and increased slightly for the older age groups (Figure 4.19.2). Furthermore, the female-to-male ratio increased with time for each age group, with the most pronounced increases in those younger than 55. In the last observation period (2003–2007), the rates in the youngest females (under age 45) were nearly 5 times higher than those in males of the same age.

FIGURE 4.19.2
Age-standardized incidence rates (ASIRs) for thyroid cancer by age group, Canada, 1983–2032 (red lines denote males, blue lines denote females)

Age-standardized incidence rates (ASIRs) for thyroid cancer by age group (males, females), Canada, 1983–2032

[Click to enlarge]

[FIGURE 4.19.2, Text Equivalent]

Health Promotion and Chronic Disease Prevention in Canada - Volume 35 · Supplement 1 · Spring 2015

FIGURE 4.19.2
Age-standardized incidence rates (ASIRs) for thyroid cancer by age group, Canada, 1983-2032

Through the entire observation period, the ASIRs of thyroid cancer were higher in females than in males in all age groups. The female-to-male ratio was highest in the youngest age group (<45), decreased steadily with age up to age 74 and increased slightly for the older age groups. Furthermore, the female-to-male ratio increased with time for each age group, with the most pronounced increases in those younger than 55. The observed increasing pattern of thyroid cancer ASIRs continued into the prediction periods in each age group in both sexes. However, the rates for both sexes are expected to reach their peak after 10 years in the youngest age group and after 20 years in 45-54 year age group.

The observed increasing pattern of thyroid cancer ASIRs continued into the prediction periods in each age group in both sexes. However, the rates for both sexes are expected to reach their peak after 10 years in the youngest age group and after 20 years in 45–54 year age group (Figure 4.19.2). The rates are projected to increase in all regions, with the most prominent increase in Ontario and the least evident one in British Columbia (Figure 4.19.1). Internal ranking of ASIRs according to region is projected to be similar for males and females, with the highest rates in Ontario and the lowest in British Columbia.

From 2003–2007 to 2028–2032, the ASIRs of thyroid cancer for Canada are projected to increase by 55% in males, from 4.5 to 7.0 per 100 000, and by 65% in females, from 16.1 to 26.5 per 100 000 (Tables 4.19.3 and 4.19.4). The annual number of new cases is estimated to increase by 139% in males, from 795 to 1895, and by 146% in females from 2810 to 6910 (Tables 4.19.1 and 4.19.2).

Comments

The significantly increasing thyroid cancer incidence rates in Canada are similar to trends observed in other developed nations.Endnote 257, Endnote 258, Endnote 259 Increased diagnostic scrutiny may have resulted in this observed increase. Advanced diagnostic technologies (e.g. ultrasonography, computed tomography scan, magnetic resonance imaging and fine-needle aspiration biopsy) have facilitated the detection of small, subclinical thyroid carcinomas.Endnote 260 More frequent use of these technologies to diagnose benign thyroid diseases, which affect more females than males, may account for the more rapid increase of thyroid cancer in females.Endnote 260, Endnote 261

Although US evidence supports the theory that the increase in thyroid cancer incidence reflects the increased detection of subclinical disease,Endnote 258 some investigators suggest that this increase is not based simply on greater detection, and that the changing prevalence of a known or an emerging risk factor may also explain this rise.Endnote 259 Risk of thyroid cancer has been linked to environmental sources of ionizing radiation, insufficient or excess iodine consumption, and heredity.Endnote 111, Endnote 262, Endnote 263 Increasing population exposure to diagnostic ionizing radiation may have increased the risk of thyroid cancer. Ionizing radiation was used to treat benign conditions in children and adolescents between 1930 and 1960.Endnote 264, Endnote 265 This use may explain some of the increase in thyroid cancer incidence in older women. A recent systematic review also supported a positive association of BMI with thyroid cancer risk.Endnote 266 Obesity rates have been increasing over the last 30 years in Canada,Endnote 51, Endnote 72, Endnote 73 and the increasing trend in obesity in the general population may be an important contributing factor in the rising thyroid cancer incidence.

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