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Table 2 SIRs for contralateral breast cancer among 1-year survivors of a first primary breast cancer in 12 SEER registries, 1992–2016

From: Risk of contralateral breast cancer according to first breast cancer characteristics among women in the USA, 1992–2016

First breast cancer characteristic No. of CBCs (%) SIR (95% CI)
Overall 12,986 (100.0) 2.21 (2.17 to 2.25)
Age at diagnosis, years
 < 40 1002 (7.7) 6.41 (6.02 to 6.82)
 40 to < 50 2691 (20.7) 2.79 (2.69 to 2.90)
 50 to < 60 3452 (26.6) 2.07 (2.00 to 2.14)
 60 to < 70 3292 (25.4) 1.91 (1.85 to 1.98)
 ≥ 70 2549 (19.6) 1.87 (1.80 to 1.94)
Time since diagnosis
 < 5 years 4620 (35.6) 2.03 (1.97 to 2.09)
 ≥ 5 years 8366 (64.4) 2.32 (2.27 to 2.37)
Stage at diagnosis
 I 6899 (53.1) 2.08 (2.03 to 2.13)
 II 4364 (33.6) 2.21 (2.14 to 2.28)
 III 1723 (13.3) 2.97 (2.83 to 3.11)
Histology
 Ductal 9340 (71.9) 2.17 (2.13 to 2.21)
 Lobular 1037 (8.0) 2.06 (1.94 to 2.19)
 Mixed 1126 (8.7) 2.49 (2.35 to 2.64)
 Other 1483 (11.4) 2.44 (2.32 to 2.57)
ER status
 Positive 8372 (64.5) 1.98 (1.94 to 2.02)
 Negative 3024 (23.3) 3.05 (2.94 to 3.16)
Initial treatment
 Radiation therapy
  Yes 7180 (55.3) 2.25 (2.20 to 2.30)
  No/unknown 5806 (44.7) 2.17 (2.11 to 2.23)
 Chemotherapy
  Yes 5086 (39.2) 2.49 (2.42 to 2.56)
  No/unknown 7900 (60.8) 2.06 (2.01 to 2.11)
 Hormone therapy
  Yes 4442 (34.2) 1.88 (1.83 to 1.94)
  No/unknown 8544 (65.8) 2.43 (2.38 to 2.48)
HER2 statusa
 Positive 93 (11.8) 1.45 (1.17 to 1.78)
 Negative 646 (82.2) 1.57 (1.45 to 1.70)
Breast cancer subtypea,b
 HR+/HER2+ 66 (8.4) 1.47 (1.14 to 1.87)
 HR+/HER2− 534 (67.9) 1.47 (1.35 to 1.60)
 HR−/HER2+ 27 (3.4) 1.42 (0.94 to 2.07)
 HR−/HER2− (triple negative) 111 (14.1) 2.43 (2.00 to 2.93)
  1. SEER, Surveillance, Epidemiology, and End Results; CBC, contralateral breast cancer; SIRs, standardized incidence ratios; CI, confidence interval; ER, estrogen receptor; HER2, human epidermal growth factor receptor 2; HR, hormone receptor; PR, progesterone receptor
  2. aHER2 status routinely collected in 2010 and onwards. Estimates include first breast cancers diagnosed between 2010 and 2015 and followed through 2016 (no. of first breast cancers = 115,835; no. of contralateral breast cancers = 786; overall SIR = 1.57, 95% CI = 1.46–1.68)
  3. bHR+ = ER+ and/or PR+; HR− = ER− and PR−
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