Can high nodal burden (≥4 axillary metastases/≥N2) be predicted without completion axillary lymph node dissection (CALND) in patients with luminal ERBB2-negative tumors and, separately, in those with invasive lobular carcinoma, and 1 or 2 sentinel lymph node (SLN) macrometastases? The gene discussed is ERBB2; the disease is invasive lobular breast carcinoma.