Table 2.

Risk of Basal-Cell Carcinoma According to Selected Risk Factors in Age- and Multivariate-adjusted Analyses, Nurses' Health Study (1986–2006) and Health Professionals' Follow-up Study (1988–2006)

	Nurses' Health Study						Health Professionals' Follow-up Study						Pooled Analysis
	No. of Cases	Person-Years	RR1a	95% CI	RR2b	95% CI	No. of Cases	Person-Years	RR1a	95% CI	RR2b	95% CI	RR2b	95% CI	P for Heterogeneityc
Family history of melanoma
No	14,023	1,538,273	1.00	Referent	1.00	Referent	7,830	626,925	1.00	Referent	1.00	Referent	1.00	Referent
Yes	1,650	132,215	1.39	1.32, 1.46	1.32	1.26, 1.39	440	27,466	1.31	1.19, 1.45	1.25	1.14, 1.38	1.31	1.25, 1.37
P value			<0.0001		<0.0001				<0.0001		<0.0001		<0.0001		0.34
Hair color
Red	836	54,505	1.52	1.41, 1.63	1.30	1.20, 1.40	228	13,356	1.17	1.02, 1.34	1.05	0.91, 1.20	1.17	0.95, 1.45
Blond	1,925	157,659	1.19	1.13, 1.25	1.13	1.07, 1.19	873	56,137	1.09	1.01, 1.18	1.05	0.97, 1.13	1.09	1.02, 1.18
Light brown	5,488	548,261	1.00	Referent	1.00	Referent	2,385	170,277	1.00	Referent	1.00	Referent	1.00	Referent
Dark brown	5,243	616,559	0.86	0.83, 0.89	0.90	0.86, 0.93	2,662	222,992	0.85	0.80, 0.90	0.89	0.84, 0.94	0.89	0.87, 0.92
Black	331	44,295	0.70	0.62, 0.78	0.74	0.66, 0.83	597	48,578	0.83	0.76, 0.91	0.91	0.83, 1.00	0.83	0.67, 1.01
Ptrend			<0.0001		<0.0001				<0.0001		<0.0001		<0.0001		0.001
No. of moles on extremity
0	7,319	787,881	1.00	Referent	1.00	Referent	3,710	292,423	1.00	Referent	1.00	Referent	1.00	Referent
1–2	3,180	299,303	1.18	1.13, 1.23	1.16	1.11, 1.21	1,196	85,071	1.11	1.04, 1.18	1.10	1.03, 1.17	1.13	1.08, 1.20
3–5	1,146	97,628	1.30	1.22, 1.38	1.26	1.19, 1.35	498	32,513	1.18	1.07, 1.30	1.15	1.05, 1.26	1.21	1.11, 1.33
≥6	704	55,420	1.44	1.33, 1.55	1.37	1.27, 1.49	344	22,955	1.15	1.03, 1.29	1.11	0.99, 1.23	1.24	1.00, 1.53
Ptrend			<0.0001		<0.0001				<0.0001		0.0008		<0.0001		0.001
Susceptibility to sunburn as a child/adolescent
No burn/some redness	7,742	915,653	1.00	Referent	1.00	Referent	1,633	160,724	1.00	Referent	1.00	Referent	1.00	Referent
Burn	3,554	309,363	1.36	1.31, 1.42	1.22	1.17, 1.28	3,316	240,393	1.37	1.29, 1.45	1.31	1.23, 1.39	1.26	1.18, 1.35
Painful/blistering burn	2,530	197,355	1.54	1.47, 1.61	1.27	1.21, 1.33	2,081	130,137	1.57	1.47, 1.68	1.44	1.34, 1.54	1.35	1.19, 1.52
Ptrend			<0.0001		<0.0001				<0.0001		<0.0001		<0.0001		0.02
Lifetime no. of severe/ blistering sunburns
0	7,136	829,350	1.00	Referent	1.00	Referent	941	85,730	1.00	Referent	1.00	Referent	1.00	Referent
1–2	2,831	277,184	1.29	1.24, 1.35	1.22	1.17, 1.28	1,625	130,054	1.13	1.05, 1.23	1.08	1.00, 1.18	1.16	1.03, 1.30
3–5	1,296	105,991	1.59	1.50, 1.69	1.44	1.36, 1.53	1,751	128,234	1.25	1.15, 1.35	1.14	1.05, 1.23	1.28	1.02, 1.62
≥6	1,293	91,698	1.83	1.72, 1.94	1.55	1.46, 1.65	2,751	188,876	1.36	1.26, 1.46	1.16	1.07, 1.25	1.34	1.01, 1.78
Ptrend			<0.0001		<0.0001				<0.0001		0.0001		<0.0001		<0.0001

Abbreviations: CI, confidence interval; RR, relative risk.

^a Adjusted for age.

^b Multivariate analysis controlled for age, family history of melanoma, natural hair color, number of moles on an extremity, susceptibility to sunburn as a child/adolescent, lifetime number of severe/blistering sunburns, and cumulative midrange ultraviolet B flux exposure.

^c P value from a test of heterogeneity between studies.