In the subset of women diagnosed with a first breast cancer between 2010 and 2015 and followed through 2016 (overall SIR = 1.57; 95% CI = 1.46–1.68; Table 2), SIRs for CBC were similar by HER2 status of the first breast cancer (HER2-positive: SIR = 1.45, 95% CI = 1.17–1.78; HER2-negative: SIR = 1.57, 95% CI = 1.45–1.70). Here, ERBB2 is linked to breast cancer.