Table 2

Distribution of type of menopause with associated RRs of breast cancer

WAANHJAL-USL-NUSRRaPa
All womenb
 Natural62.7%51.4%63.8%69.2%60.5%72.6%
 Bilateral oophorectomy18.6%21.1%18.3%17.8%16.1%10.8%
 Simple hysterectomy18.7%27.5%17.8%12.9%23.5%16.6%
Excluding women with simple hysterectomyc
 Natural77.3%70.8%77.8%79.5%79.1%87.1%
 Bilateral oophorectomy22.7%29.1%22.2%20.5%20.9%12.9%
 Age at natural menopause (yrs)
  ≤4411.7%14.7%15.0%9.0%16.8%20.6%1.00
  45–4924.8%22.3%23.0%22.3%25.4%30.1%1.04
  50–5432.5%26.0%30.0%38.4%30.1%29.2%1.21
  55+8.2%7.9%9.8%9.8%6.7%7.2%1.31
 Age at bilateral oophorectomy (yrs)
  ≤4413.1%19.0%12.8%10.0%12.6%7.6%0.84
  45–496.4%7.2%6.2%7.2%5.6%3.6%0.97
  50+3.2%3.0%3.2%3.4%2.8%1.7%1.040.002d
  • a P = two-sided significance test; RR, RRs fitting all seven known risk factors and ethnicity to data on women with natural menopause or bilateral oophorectomy.

  • b Standardized to the age distribution of the cohort as in Table 1<$REFLINK> .

  • c Standardized to the age distribution of the remaining cohort.

  • d Test for type of menopause and separate linear trends for age at natural menopause and age at bilateral oophorectomy (3 degrees of freedom) after fitting all seven known risk factors and ethnicity.