Smoking and risk of breast cancer in the Generations Study cohort

Jones, Michael E.; Schoemaker, Minouk J.; Wright, Lauren B.; Ashworth, Alan; Swerdlow, Anthony J.

doi:10.1186/s13058-017-0908-4

Breast Cancer Research

Table 3 Relative risk of breast cancer in relation to smoking in relation to age at start of smoking, by oestrogen receptor status

From: Smoking and risk of breast cancer in the Generations Study cohort

	Oestrogen receptor status								All breast cancer^a
	Positive				Negative
	Cases	HR^b	95% CI	P value	Cases	HR^b	95% CI	P value	Cases	HR^b	95% CI	P value
Age started smoking, years^c
Never smoked	898	1.00	Baseline		167	1.00	Baseline		1073	1.00	Baseline
< 17	218	1.25	1.08–1.46	0.0032	42	1.22	0.87–1.72	0.25	261	1.24	1.08–1.43	0.0023
17–19	249	1.13	0.98–1.30	0.093	54	1.32	0.97–1.80	0.077	304	1.15	1.01–1.31	0.030
20+	122	0.95	0.79–1.15	0.62	28	1.25	0.84–1.87	0.28	151	1.00	0.84–1.18	0.96
Age unknown	22	0.94	0.62–1.44	0.79	3	0.73	0.23–2.30	0.59	26	0.94	0.64–1.39	0.76
	Trend^d P = 0.17				Trend^d P = 0.74				Trend among ever smokers^d P = 0.18
	Trend interaction P = 0.30
Cigarettes per day at ages 16–24 years (among those aged ≥ 25 years at entry)
Never smoked	895	1.00	Baseline		166	1.00	Baseline		1069	1.00	Baseline
1–4	77	1.10	0.87–1.39	0.42	21	1.65	1.05–2.60	0.032	99	1.19	0.97–1.46	0.10
5–9	131	1.23	1.02–1.48	0.027	18	0.92	0.57–1.50	0.75	149	1.16	0.99–1.40	0.069
10–14	170	1.11	0.94–1.31	0.22	31	1.07	0.73–1.57	0.73	203	1.10	0.95–1.29	0.21
15+	169	1.13	0.96–1.34	0.14	42	1.44	1.02–2.03	0.038	212	1.18	1.01–1.37	0.034
Started at age 25+	31	0.91	0.64–1.31	0.62	7	1.22	0.57–2.60	0.61	38	0.95	0.69–1.31	0.75
Unknown	31	0.97	0.68–1.39	0.87	7	1.32	0.62–2.79	0.47	38	1.01	0.73–1.40	0.95
	Trend^d P = 0.70				Trend^d P = 0.65				Trend^d P = 0.78
	Trend interaction P = 0.81
Starting smoking relative to age at menarche, years
Never smoked	898	1.00	Baseline		167	1.00	Baseline		1073	1.00	Baseline
At or before menarche	32	1.60	1.12–2.28	0.010	2	0.50	0.12–2.02	0.33	34	1.40	0.98–1.99	0.061
Years started after menarche
1–4	217	1.21	1.04–1.41	0.015	48	1.38	1.00–1.91	0.049	266	1.23	1.07–1.41	0.0040
5–9	239	1.09	0.94–1.27	0.23	54	1.35	0.99–1.84	0.060	295	1.13	0.99–1.29	0.071
10–14	36	1.03	0.74–1.44	0.86	7	1.13	0.53–2.43	0.75	43	1.04	0.76–1.41	0.82
15+	12	0.64	0.36–1.13	0.12	6	1.92	0.85–4.34	0.12	18	0.81	0.51–1.30	0.39
Interval unknown	75	1.02	0.79–1.32	0.88	10	0.74	0.38–1.41	0.35	86	0.99	0.77–1.27	0.92
	Trend^d P = 0.041				Trend^d P = 0.80				Trend^d P = 0.031
	Trend for interaction P = 0.42
Starting smoking relative to age at thelarche, years
Never smoked	898	1.00	Baseline		167	1.00	Baseline		1073	1.00	Baseline
At or before thelarche	16	1.45	0.88–2.39	0.14	1	0.45	0.06–3.24	0.43	17	1.27	0.79–2.06	0.33
Years started after thelarche
1–4	160	1.17	0.99–1.39	0.075	31	1.17	0.79–1.72	0.43	192	1.17	1.00–1.37	0.056
5–9	238	1.06	0.92–1.22	0.47	60	1.42	1.06–1.91	0.020	300	1.11	0.98–1.27	0.10
10–14	37	0.98	0.70–1.36	0.90	11	1.60	0.87–2.95	0.13	48	1.07	0.80–1.43	0.66
15+	18	0.94	0.59–1.50	0.79	6	1.83	0.81–4.14	0.14	24	1.06	0.71–1.59	0.77
Interval unknown	142	1.22	1.02–1.46	0.031	18	0.87	0.53–1.42	0.59	161	1.17	0.99–1.38	0.074
	Trend^d P = 0.58				Trend^d P = 0.35				Trend among ever smokers^d P = 0.82
	Trend for interaction P = 0.28
Starting smoking relative to first childbirth, among parous (follow-up time only from first childbirth)
Never smoked	772	1.00	Baseline		148	1.00	Baseline		927	1.00	Baseline
After first childbirth	34	1.20	0.85–1.71	0.30	9	1.85	0.94–3.67	0.076	43	1.28	0.94–1.76	0.12
Interval from starting smoking to first childbirth, years
1–4	73	1.12	0.88–1.44	0.35	15	1.28	0.74–2.21	0.38	89	1.14	0.91–1.45	0.23
5–9	177	1.06	0.90–1.25	0.51	42	1.35	0.96–1.90	0.089	220	1.10	0.94–1.28	0.22
10–14	130	1.08	0.89–1.30	0.42	22	0.89	0.57–1.40	0.62	152	1.04	0.87–1.24	0.65
15+	77	1.17	0.91–1.51	0.21	16	1.13	0.66–1.92	0.65	94	1.17	0.93–1.47	0.19
Interval unknown	22	1.07	0.70–1.64	0.75	2	0.54	0.13–2.17	0.38	25	1.02	0.69–1.52	0.92
	Trend^d P = 0.72				Trend^d P = 0.33				Trend among ever smokers^d P = 0.97
	Trend for interaction P = 0.27

^aIncludes 21 breast cancers with unknown or unmeasured oestrogen receptor status
^bAdjusted for attained age (Cox regression time scale); time since recruitment to cohort (0, 1–2, 3+ years); birth cohort (1908–1939, 1940–1949, 1950–1959, 1960–1969, 1970–1996); benign breast disease (yes/no); family history of breast cancer in first-degree relatives (yes/no); socio-economic score (Acorn score as trend, missing); age at menarche (trend, missing); age at first pregnancy (trend, missing); parity (trend, missing); duration of breastfeeding (trend, missing); current oral contraceptive use before menopause (yes/no); alcohol consumption (never regular, trend current drinker 1 to < 60 g/day, current drinker ≥ 60 g/day, past drinker, drinker with unknown details); physical activity [log(metabolic equivalent) trend, missing]; pre-menopausal body mass index at age 20 years (trend, missing); post-menopausal body mass index (trend, missing); menopausal hormone therapy use (never used, ex-user, current oestrogen-only user, current oestrogen plus progestogen user, current user of other types, missing); menopausal status (pre- or post-menopausal) and age at menopause (trend, missing)
^cTime updated through follow-up period
^dTrend excludes never smoker and unknown group

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