Table 4.
Hazard ratios and 95% confidence intervals for papillary and follicular thyroid cancer according to hormonal and reproductive factors
| Papillary thyroid cancer |
Follicular thyroid cancer |
|||||
|---|---|---|---|---|---|---|
| Factor | Cases | Person-years | HR a (95% CI) | Cases | Person-years | HR a (95% CI) |
| Age at menarche, years | ||||||
| <10 | 66 | 327 175 | 1.23 (0.94–1.60) | 12 | 327 175 | 1.68 (0.89–3.16) |
| 10–11 | 424 | 2 976 607 | 1 (reference) | 58 | 2 976 607 | 1 (reference) |
| 12 to <14 | 900 | 6 916 907 | 0.99 (0.88–1.11) | 118 | 6 916 907 | 1.00 (0.73–1.39) |
| 14 to <16 | 352 | 3 244 178 | 0.88 (0.76–1.03) | 60 | 3 244 178 | 1.15 (0.79–1.70) |
| ≥16 | 114 | 816 317 | 1.06 (0.85–1.34) | 14 | 816 317 | 1.24 (0.66–2.31) |
| Unknown | 24 | 260 635 | 0.83 (0.55–1.26) | 0 | 260 635 | – |
| P-trend = 0.15 | P-trend = 0.60 | |||||
| Continuous (per year) | 0.98 (0.95–1.01) | 1.02 (0.95–1.11) | ||||
| Parity | ||||||
| 0 | 259 | 2 073 725 | 0.86 (0.72–1.02) | 34 | 2 073 725 | 1.19 (0.71–1.99) |
| 1 | 309 | 2 103 623 | 1 (reference) | 30 | 2 103 623 | 1 (reference) |
| 2 | 628 | 4 590 952 | 0.98 (0.85–1.14) | 91 | 4 590 952 | 1.30 (0.84–2.00) |
| 3–4 | 518 | 4 327 991 | 0.88 (0.75–1.03) | 80 | 4 327 991 | 1.07 (0.68–1.67) |
| ≥5 | 118 | 1 020 111 | 0.87 (0.69–1.09) | 20 | 1 020 111 | 0.97 (0.53–1.77) |
| Unknown | 48 | 425 418 | 0.83 (0.61–1.14) | 7 | 425 418 | 0.95 (0.40–2.25) |
| P-trend = 0.19 | P-trend = 0.70 | |||||
| Continuous (per live birth)b | 1.00 (0.97–1.03) | 0.96 (0.89–1.04) | ||||
| Oral contraceptive use | ||||||
| Never | 794 | 6 689 707 | 1 (reference) | 133 | 6 689 707 | 0.97 (0.74–1.28) |
| Ever | 1052 | 7 584 294 | 1.11 (1.00–1.24) | 125 | 7 584 294 | 0.60 (0.20–1.75) |
| Unknown | 34 | 267 818 | 1.03 (0.72–1.48) | 4 | 267 818 | 1.11 (0.54–2.28) |
| Duration of oral contraceptive use (years) | ||||||
| <5 | 531 | 3 787 714 | 1 (reference) | 63 | 3 787 714 | 1 (reference) |
| ≥5 | 471 | 3 445 763 | 0.85 (0.75–0.97) | 57 | 3 445 763 | 0.87 (0.60–1.25) |
| Unknown | 50 | 350 818 | 1.33 (0.98–1.81) | 5 | 350 818 | 0.67 (0.25–1.82) |
| Hysterectomy | ||||||
| No | 1229 | 10 013 122 | 1 (reference) | 171 | 10 013 122 | 1 (reference) |
| Yes | 515 | 3 218 411 | 1.28 (1.14–1.43) | 71 | 3 218 411 | 1.07 (0.80–1.44) |
| Unknown | 50 | 724 542 | 0.67 (0.50–0.90) | 10 | 724 542 | 0.63 (0.32–1.24) |
| Oophorectomy | ||||||
| No | 1432 | 11 018 045 | 1 (reference) | 198 | 11 018 045 | 1 (reference) |
| Unilateral | 92 | 650 402 | 1.11 (0.90–1.38) | 10 | 650 402 | 0.75 (0.40–1.42) |
| Bilateral | 253 | 1 632 944 | 1.16 (1.01–1.33) | 35 | 1 632 944 | 0.98 (0.68–1.43) |
| Yes, number of ovaries removed unknown | 8 | 35 911 | 1.35 (0.66–2.76) | 1 | 35 911 | 2.23 (0.29–17.32) |
| Unknown | 95 | 1 204 518 | 0.74 (0.59–0.93) | 18 | 1 204 518 | 0.57 (0.32–1.02) |
| Menopausal status | ||||||
| Pre-menopausal | 537 | 3 422 628 | 1 (reference) | 52 | 3 422 628 | 1 (reference) |
| Post-menopausal | 1106 | 8 807 350 | 0.82 (0.70–0.97) | 170 | 8 807 350 | 0.81 (0.50–1.30) |
| Unknown | 159 | 1 054 167 | 1.04 (0.85–1.27) | 25 | 1 054 167 | 1.07 (0.63–1.82) |
| Age at menopausec (years) | ||||||
| <40 | 158 | 999 112 | 1.29 (1.02–1.62) | 20 | 999 112 | 1.47 (0.75–2.87) |
| 40–44 | 136 | 1 138 789 | 1 (reference) | 15 | 1 138 789 | 1 (reference) |
| 45 to <50 | 284 | 2 437 133 | 1.00 (0.82–1.23) | 45 | 2 437 133 | 1.54 (0.85–2.77) |
| 50 to <55 | 395 | 3 318 156 | 1.04 (0.86–1.27) | 63 | 3 318 156 | 1.62 (0.91–2.86) |
| ≥55 | 113 | 803 705 | 1.19 (0.92–1.54) | 24 | 803 705 | 2.63 (1.37–5.07) |
| Unknown | 97 | 702 735 | 1.28 (0.97–1.69) | 14 | 702 735 | 2.09 (0.97–4.52) |
| P-trend = 0.05 | P-trend = 0.08 | |||||
| Continuous (per year)c | 1.00 (0.99–1.01) | 1.02 (1.00–1.05) | ||||
| Menopausal hormone therapy usec | ||||||
| Never | 406 | 3 780 032 | 1 (reference) | 79 | 3 780 032 | 1 (reference) |
| Ever | 610 | 4 356 044 | 1.17 (1.03–1.34) | 88 | 4 356 044 | 1.07 (0.78–1.47) |
| Unknown | 13 | 159 025 | 0.81 (0.46–1.41) | 0 | 159 025 | 0.00 (0.00–0.00) |
| Duration of menopausal hormone therapy usec (years) | ||||||
| ≤5 | 246 | 1 664 767 | 1 (reference) | 29 | 1 664 767 | 1 (reference) |
| >5 | 264 | 1 710 651 | 0.93 (0.76–1.15) | 41 | 1 710 651 | 1.33 (0.77–2.30) |
| Unknown | 12 | 177 700 | 0.77 (0.42–1.42) | 1 | 177 700 | 0.67 (0.09–5.10) |
| Reproductive yearsc | ||||||
| Quartile 1 (0 to <31 years) | 302 | 2 190 834 | 1 (reference) | 38 | 2 190 834 | 1 (reference) |
| Quartile 2 (31 to <36 years) | 194 | 1 749 059 | 0.85 (0.71–1.02) | 31 | 1 749 059 | 1.15 (0.71–1.87) |
| Quartile 3 (36 to <39 years) | 198 | 1 796 601 | 0.87 (0.72–1.04) | 37 | 1 796 601 | 1.35 (0.85–2.15) |
| Quartile 4 (≥39 years) | 386 | 2 892 888 | 0.95 (0.81–1.11) | 61 | 2 892 888 | 1.30 (0.86–1.96) |
| P-trend = 0.25 | P-trend = 0.22 | |||||
| Continuous (per year) | 1.00 (0.99–1.01) | 1.02 (0.99–1.04) | ||||
| Ovulatory cyclesc | ||||||
| Quartile 1 (0 to <320) | 223 | 1 553 939 | 1 (reference) | 28 | 1 553 939 | 1 (reference) |
| Quartile 2 (320 to <402) | 187 | 1 551 509 | 0.85 (0.70–1.03) | 25 | 1 551 509 | 0.92 (0.53–1.59) |
| Quartile 3 (402 to <467) | 217 | 1 601 262 | 0.96 (0.80–1.16) | 40 | 1 601 262 | 1.42 (0.87–2.33) |
| Quartile 4 (≥467) | 195 | 1 607 859 | 0.82 (0.67–1.01) | 40 | 1 607 859 | 1.37 (0.83–2.27) |
| P-trend = 0.15 | P-trend = 0.23 | |||||
| Continuous (per cycle) | 1.00 (1.00–1.00) | 1.00 (1.00–1.00) | ||||
HR, hazard ratio.
P-trend calculated using the Wald test for the exposure term modelled continuously using ordinal groups.
a
Adjusted for attained age (used as time metric), race, education, body mass index, alcohol intake and smoking.
b
Restricted to women with at least one live birth.
c
Restricted to post-menopausal women.