Table 3. Relative hazards (HRs) of breast cancers by the initial age of exposure.

Risk groups	Cases	Person years	Incidence (10 000 py)	HR	90% CI of HR	P-value
IAE >20 years old
TCD <5 mSv	10	14131	7.1	1
TCD 5–100 mSv	11	19816	5.6	0.88	0.43, 1.82	0.76
TCD ⩾100 mSv	7	5123	13.7	2.07	0.89, 4.62	0.14
TCD 100 mSv (test for linear trend)				1.07	0.98, 1.14	0.14
IAE ⩽20 years old
TCD <5 mSv	1	27829	0.4	1
TCD 5–100 mSv	4	26792	1.5	3.02	0.59, 31.82	0.33
TCD ⩾100 mSv	2	4321	4.6	10.91	1.55, 125.9	0.05
TCD 100 mSv (test for linear trend)				1.38	1.14, 1.60	0.0008

Abbreviations: CI=confidence interval; HR=Hazards ratio; IAE=initial age at exposure; TCD=Taiwan Cumulative Dose; person-years accounted for minimum latent periods as stated in Table 2.

Breast cancers with minimum latent periods 10 years.