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. Author manuscript; available in PMC: 2019 Sep 25.
Published in final edited form as: Ann Intern Med. 2018 Dec 11;170(1):22–30. doi: 10.7326/M18-1323

Figure 5. HR for ER-positive and ER-negative breast cancer according to years since most recent birth, adjusted for attained age, study, and parity (continuous).

Figure 5.

Nulliparous women are the reference group. Dashed curves correspond to 95% CIs. Vertical lines represent the quadratic spline knots at 6.1, 13.3, 18.4, 23.3, and 29.3 y after birth. Tests for interaction with ER status were statistically significant (P < 0.001). ER-negative breast cancer risk peaked 2.2 y after birth (HR, 1.77 [95% CI, 1.34 to 2.33]), and the HR decreased to 1.38 (CI, 1.01 to 1.88) at 34.5 y after birth but did not cross over to a protective association. ER-positive breast cancer had a peak HR of 1.88 (CI, 1.62 to 2.20) at 5.3 y, crossing the null value at 25.0 y and reaching an HR of 0.90 (CI, 0.74 to 1.09) at 34.5 y. ER = estrogen receptor; HR = hazard ratio.