Table 3. Familial cancer risks for people with multiple affected relatives.

	Family history	Cancer site
		Colorectum	Lung	Breast	Prostate	Urinarybladder	Melanoma	Nervous system
Case numbers1, Relative risk, 95%CI	Both parents affected	63	25	11	0	6	8	3
		1.98 (1.46–2.69)	3.02 (1.86–4.92)	9.49 (4.58–19.67)		3.50 (0.92–13.28)	6.00 (2.54–14.15)	3.64 (0.82–16.17)
	1 parent and 1 sibling affected	186	42	485	930	12	50	24
		3.67 (3.07–4.39)	2.48 (1.70–3.61)	2.88 (2.58–3.21)	4.59 (4.23–4.98)	2.86 (1.11–7.35)	8.20 (5.81–11.56)	9.47 (5.59–16.05)
	2 siblings affected	33	27	199	368	3	15	0
		2.57 (1.68–3.91)	3.39 (2.12–5.42)	2.50 (2.11–2.97)	5.25 (4.62–5.98)	2.74 (0.42–18.03)	4.47 (2.39–8.37)
	3 siblings affected	4	4	4	44	0	0	0
		6.59 (1.97–22.08)	20.84 (6.17–70.38)	1.02 (0.30–3.41)	6.78 (4.68–9.83)
P-values for differences among RRs2	Both parents vs. 1 parent	0.36	0.0528	<.0001		0.31	0.0398	0.26
	1 Parent and 1 sibling vs. 1 parent	<.0001	0.14	<.0001	<.0001	0.32	<.0001	<.0001
	1 Parent and 1 sibling vs. 1 sibling	<.0001	0.95	<.0001	<.0001	0.41	<.0001	<.0001
	2 siblings vs. 1 sibling	0.25	0.22	0.0006	<.0001	0.71	0.13
	3 siblings vs. 1 sibling	0.0528	0.0007	0.34	<.0001
	3 siblings vs. 2 sibling	0.15	0.0063	0.15	0.20
	1 Parent and 1 sibling vs. 2 siblings	0.12	0.31	0.18	0.08	0.97	0.10
	1 Parent and 1 sibling vs. both parents	0.0006	0.53	0.0015		0.81	0.51	0.24
	2 siblings vs. both parents	0.33	0.74	0.0005		0.83	0.59

¹Number of concordant cases

²P-values from Wald chi-square statistics testing for pairwise differences among RRs for different family histories.