ERBB2 and neoplasm: The number of 30-d intervals for cT1a, cT1b, cT1c, and cT2 tumors to grow 1 mm was 3.95, 2.63, 2.27, and 1.92, respectively, with tumor growth faster in TN tumors (1.29) than HER2+ (4.95) or HR+ (2.35) (P < 0.0001).<h4>Conclusions</h4>Longer delays risk greater upstaging and nodal spread, explaining the association with higher disease-specific and overall mortality in prior studies.