ERBB2 and breast cancer: 5-year IDFS showed no difference between low Ki67 (88.9%; 95% CI 75.5-100%), intermediate Ki67 (82.0%; 95% CI 72.6-92.7%), and high Ki67 (80.9%, 95% CI 70.1-92.3%) subgroups (p = 0.7).<h4>Conclusion</h4>In HER2-positive breast cancer, the Ki67-score showed no association with either pCR or IDFS, thereby questioning its clinical utility.