Table 4.

Relative risk of breast cancer according to age of infectious mononucleosis onset in NHS II by median age at breast cancer diagnosis and menopausal status, 1989–2007

	RR and (95% CI)
Age at IM	No IM	≤15	16–19	20–24	25–29	30+
Age at BC dx <48.9y*
Cases/ person year	966 / 961,710	43/50,655	98/90,730	50/40,375	16/11,748	17/15,819
Age Adjusted RR†	1.00	0.88(0.65–1.20)	1.09(0.88–1.34)	1.21(0.91–1.61)	1.38(0.84–2.26)	1.05(0.65–1.70)
Multivariable RR§	1.00	0.85(0.63–1.15)	1.05(0.85–1.29)	1.15(0.86–1.52)	1.36(0.83–2.23)	1.06(0.66–1.71)
Age at BC dx =>48.9y
Cases/ person year	961 / 346,999	26/13,791	88/30,483	42/15,811	17/3,990	17/6,285
Age Adjusted RR†	1.00	0.70(0.48–1.04)	1.05(0.85–1.31)	0.96(0.70–1.30)	1.53(0.95–2.47)	0.98(0.61–1.58)
Multivariable RR§	1.00	0.69(0.46–1.01)	1.02(0.82–1.26)	0.91(0.67–1.25)	1.58(0.98–2.56)	0.98(0.61–1.58)
Premenopausal
Cases/ person year	1,246 / 951,341	44/47,982	113/89,459	58/40,256	20/11,463	21/14,903
Age Adjusted RR†*	1.00	0.75(0.56–1.02)	0.98(0.81–1.19)	1.07(0.83–1.40)	1.39(0.89–2.15)	1.08(0.70–1.67)
Multivariable RR§*	1.00	0.73(0.54–0.99)	0.95(0.78–1.15)	1.02(0.79–1.33)	1.36(0.87–2.11)	1.07(0.70–1.65)
Post menopausal
Cases/ person year	505 / 257,088	18/11,418	51/22,738	27/11,964	12/3,170	10/5,176
Age Adjusted RR†	1.00	0.86(0.54–1.38)	1.17(0.87–1.55)	1.14(0.78–1.68)	1.98(1.12–3.51)	1.01(0.54–1.88)
Multivariable RR§	1.00	0.83(0.52–1.32)	1.12(0.84–1.50)	1.07(0.72–1.57)	1.99(1.12–3.52)	1.00(0.53–1.86)

^†Relative Risk and 95% confidence interval from age (5 year categories) adjusted Cox proportional hazards model.

^§Relative Risk and 95% confidence interval from model above (†) additionally controlling for variables mentioned in Table 2.

^*p for linear trend < 0.05, however, data suggest a non-linear relation and trend is driven by increased risk in 25–29 category.

^*48.9 median age at breast cancer diagnosis.

^*p for linear trend < 0.05, however, data suggest a non-linear relation and trend is driven by increased risk in 25–29 category.