Hyperthyroidism is associated with breast cancer risk and mammographic and genetic risk predictors

Table 1 Risk of breast cancer in women in the national and KARMA cohorts with a diagnosis of hyperthyroidism, compared to women without hyperthyroidism

	Swedish national cohort N = 3,793,492 (2002–2011)			KARMA cohort N = 69,598 (2002–2017)
	No. HT	No. BC	IRR (95% CI) Model 1	No. HT	No. BC	IRR (95% CI) Model 1	IRR (95% CI) Model 2
Overall	28,136	389	1.23 (1.12–1.36)	1034	36	1.23 (0.88–1.70)	1.22 (0.88–1.70)
Premenopausal	11,298	54	1.28 (0.98–1.68)	353	6	1.14 (0.51–2.54)	1.11 (0.50–2.48)
Postmenopausal	19,668	335	1.23 (1.10–1.36)	1010	30	1.27 (0.88–1.82)	1.26 (0.88–1.81)
By age (years)
< 40	6659	25	1.51 (1.02–2.24)	106	6	3.16 (1.41–7.05)	3.14 (1.41–7.02)
40–55	7284	94	1.15 (0.94–1.41)	481	9	0.74 (0.38–1.42)	0.73 (0.38–1.40)
> 55	14,633	270	1.24 (1.10–1.40)	447	21	1.38 (0.90–2.12)	1.38 (0.90–2.13)
By years since hyperthyroidism diagnosis
0–2	28,136	123	1.23 (1.03–1.47)	1034	10	1.70 (0.92–3.17)	1.69 (0.91–3.14)
2–5	22,648	157	1.25 (1.07–1.46)	915	9	1.02 (0.53–1.96)	1.01 (0.52–1.94)
>5	14,026	109	1.21 (1.00–1.46)	696	17	1.16 (0.72–1.87)	1.16 (0.72–1.87)
By types of hyperthyroidism
Graves’ disease	16,552	201	1.17 (1.02–1.35)	736	27	1.34 (0.92–1.96)	1.33 (0.91–1.95)
Toxic nodular goiter	7113	130	1.38 (1.16–1.63)	278	13	1.43 (0.83–2.47)	1.43 (0.83–2.47)
Others or unspecified	14,592	187	1.20 (1.04–1.38)	377	7	0.78 (0.37–1.64)	0.78 (0.37–1.63)

Hyperthyroidism patients were identified by the main diagnosis given in the inpatient and outpatient registers. IRRs were calculated by comparing hyperthyroidism patients to women without hyperthyroidism using Poisson regression, using age as the underlying time scale. In the analyses stratified by menopausal status, women with age younger than 50 in the national cohort were considered as premenopausal women, while in the KARMA cohort, the exact age at menopause was used. Model 1 adjusted for calendar period, and Model 2 further adjusted for BMI, age at menarche, number of births, family history of breast cancer, hormone replacement therapy use, oral contraceptive use, and benign breast disease. Statistically significant results are bolded
HT hyperthyroidism, BC breast cancer, IRR incidence rate ratio, CI confidence interval

ISSN: 1741-7015