Table 4.

History of UL and risk of breast cancer, by stage at breast cancer diagnosis^b

	Person-years	Cases	IRR (95% CI)a
History of UL, any age
In situ breast cancer
No UL	491,368	184	1.00 (Ref.)
UL at any age	368,295	210	1.02 (0.82-1.27)
Stage 1 breast cancer
No UL	491,561	337	1.00 (Ref.)
UL at any age	368,513	376	0.99 (0.84-1.16)
Stage 2, 3 or 4 breast cancer
No UL	491,665	430	1.00 (Ref.)
UL at any age	368,519	396	0.97 (0.83-1.12)
History of UL, age<30 years
In situ breast cancer
No UL	491,368	184	1.00 (Ref.)
UL at age<30	88,302	45	1.04 (0.72-1.49)
Stage 1 breast cancer
No UL	491,561	337	1.00 (Ref.)
UL at age<30	88,350	87	1.16 (0.90-1.50)
Stage 2, 3, or 4 breast cancer
No UL	491,665	430	1.00 (Ref.)
UL at age<30	88,377	105	1.16 (0.92-1.47)

^aAdjusted for age, questionnaire cycle, menopausal status, cause of menopause, age at menopause, parity, age at first birth, years since last birth, BMI, age at menarche, female hormone use (recency and formulation), smoking, alcohol consumption, family history of breast cancer, education, and vigorous exercise.

^bThere were 160 invasive cases (80 exposed and 80 unexposed) with missing data on stage at diagnosis.