Levonorgestrel-releasing intrauterine system and the risk of breast cancer: A nationwide cohort study

Figures & data

Table I. Cohort of levonorgestrel-releasing intrauterine system (LNG-IUS) users, follow-up 1994–2012.

	Follow-up from the first LNG-IUS purchase		Follow-up from the second LNG-IUS purchase
Age	n	Women-years	n	Women-years
30 to 34	20 998	47 196	290	365
35 to 39	28 219	172 523	4 151	10 352
40 to 44	25 955	285 032	5 643	35 218
45 to 49	18 670	310 402	4 150	52 677
50 to 54	–	217 615	–	38 305
Total	93 843	1 032 767	14 234	136 917

Number of all women (n) counted by age at the purchase of LNG-IUS; women-years counted by age at the follow-up.

Table II. Observed (OBS) numbers of breast cancer cases and standardized incidence ratios (SIR, with 95% confidence interval [CI]) among Finnish women who purchased levonorgestrel-releasing intrauterine system (LNG-IUS) for menorrhagia during 1994–2007 at ages 30–49 years, by time since first purchase, 1994–2012. Follow-up from the first purchase of LNG-IUS until age 55.

Breast cancer category by histology	Time since first LNG-IUS purchase
	0–0.99 years			1–4.99 years			5–9.99 years			over 10 years			Entire follow-up
	OBS	SIR	95% CI	OBS	SIR	95% CI	OBS	SIR	95% CI	OBS	SIR	95% CI	OBS	SIR	95% CI
Lobular	12	0.93	0.48–1.61	72	0.99	0.78–1.25	168	1.40	1.20–1.62***	124	1.59	1.32–1.87***	376	1.33	1.20–1.46***
localised	6	1.09	0.40–2.37	32	1.03	0.71–1.45	73	1.40	1.10–1.76**	57	1.63	1.16–1.57***	168	1.36	1.16–1.57***
non-localised	6	0.86	0.32–1.88	37	0.97	0.68–1.33	86	1.40	1.12–1.73**	55	1.44	1.08–1.87*	184	1.27	1.10–1.46**
Ductal	66	0.90	0.69–1.14	413	1.12	1.02–1.23*	688	1.25	1.16–1.34***	431	1.26	1.14–1.38***	1598	1.20	1.14–1.25***
localised	38	1.04	0.74–1.43	229	1.26	1.10–1.42***	339	1.27	1.14–1.41***	219	1.34	1.17–1.51***	825	1.27	1.19–1.36***
non-localised	24	0.71	0.46–1.05	171	1.01	0.86–1.16	322	1.25	1.12–1.39***	188	1.19	1.03–1.36*	705	1.14	1.06–1.22***
Ductal in situ	3	0.67	0.14–1.95	34	1.13	0.78–1.57	69	1.17	0.91–1.47	52	1.26	0.94–1.65	158	1.17	1.00–1.36

*p < 0.05.

**p < 0.01.

***p < 0.001.