Table 4.
Hazard ratios and 95% CIs for the association between type 2 diabetes, metformin use and total breast cancer stratified by selected factors, The Sister Study
| Presence of T2D | T2D and Metformin use, versus no T2D | |||||
|---|---|---|---|---|---|---|
| Cases / person-years | All T2D | P interaction | All T2D | P interaction | ||
| Time varying menopausal status | Pre-menopausal | 464 / 68,733 | 0.80 (0.48-1.35) | 0.43 | 0.92 (0.50-1.68) | 0.60 |
| Post-menopausal | 2,214 / 304,932 | 1.00 (0.87-1.14) | 0.98 (0.83-1.16) | |||
| Race/ethnicity | Non-Hispanic White | 2,314 / 319,621 | 0.93 (0.80-1.08) | 0.05 | 0.94 (0.78-1.13) | 0.36 |
| Non-Hispanic Black | 189 / 29,030 | 0.99 (0.69-1.42) | 1.06 (0.70-1.61) | |||
| Other | 175 / 25,014 | 1.50 (1.02-2.19) | 1.20 (0.73-1.99) | |||
| Income | < $49,999 | 615 / 86,247 | 0.96 (0.76-1.21) | 0.66 | 0.97 (0.73-1.29) | 0.62 |
| $50,000-$99,999 | 1,019 / 149,212 | 1.00 (0.81-1.22) | 0.95 (0.74-1.23) | |||
| $100,000+ | 926 / 12,635 | 1.04 (0.80-1.35) | 1.07 (0.79-1.47) | |||
| Healthy Eating Index-2015 | < median | 1,311 / 180,607 | 1.02 (0.86-1.21) | 0.09 | 0.99 (0.80-1.21) | 0.28 |
| ≥ median | 1,301 / 182,837 | 0.95 (0.77-1.18) | 0.98 (0.76-1.28) | |||
| Time-varying BMI, kg/m2 | Non-obese (<30 and ≥18.5) | 1,857 / 266,796 | 0.97 (0.79-1.19) | 0.90 | 1.07 (0.83-1.37) | 0.40 |
| Obese (≥30) | 797 / 102,219 | 1.02 (0.86-1.21) | 0.95 (0.77-1.17) | |||
| Stronger family history * | No | 1,766 / 280,119 | 1.03 (0.88-1.21) | 0.41 | 1.06 (0.87-1.29) | 0.20 |
| Yes | 912 / 93,545 | 0.92 (0.73-1.15) | 0.84 (0.63-1.12) | |||
| Recent mammogram screening | <1y | 2,255 / 305,675 | 0.97 (0.84-1.12) | 0.38 | 0.96 (0.80-1.14) | 0.43 |
| ≥ 1y | 423 / 67,989 | 1.06 (0.78-1.43) | 1.08 (0.75-1.57) | |||
Abbreviations: T2D, type 2 diabetes; BMI, body mass index.
Adjusted for race/ethnicity (non-Hispanic white, non-Hispanic black, or other), educational attainment (high school degree or less, some college, college degree or higher), height, body mass index (BMI) at 30-39 years old (<18.5, 18.5 to <25, 25 to <30, 30 to <35, 35 to <40, or ≥40 kg/m2), physical activity (metabolic equivalent hours/week), recent mammogram screening (<1 y, 1 to 2y, >2y), age at menarche ≤11 years old, number of relatives diagnosed with breast cancer (1, ≥2), and birth cohort (born in <1945, 1945 to <1955, 1955 to <1965 or ≥1965), as well as time varying covariates including BMI, menopausal status (binary), interaction term between BMI and menopausal status, age at menopause, alcohol consumption (never drinker, former drinker, current drinker <1 drink/day, current drinker 1-1.9 drinks/day, current drinker ≥2 drinks/day), smoking status (≥20 pack-years, <20 and ≥10 pack-years, <10 and >0 pack-years, never smoker), use of any hormonal birth control (never, ever), hormone therapy (none, estrogen only, both estrogen and progesterone), age at first childbirth (nulliparous, <21 years, 21 to <25 years, 25 to <29 years, or ≥29 years), lifetime duration of breastfeeding (weeks, none and tertiles among women with any breastfeeding), and parity (0, 1, 2, ≥3 births) except each stratified variable.
No. of first-degree relatives diagnosed with breast cancer ≥2