ERBB2 and neoplasm: Proxy subtype had the strongest association with not undergoing surgery (luminal B [HER2-positive], HER2-enriched, and basal vs. luminal A, OR: 4.08 [2.72–6.12], 2.50 [1.52–4.12] and 2.03 [1.24–3.35] respectively), followed by age at diagnosis (<50 and ≥70 vs. 50–69 years, OR: 1.57 [1.30–1.89] and 2.94 [2.34–3.68] respectively) and pre-surgical tumor size (21–50 mm and >50 mm vs. <20 mm, OR: 2.23 [1.85–2.68] and 2.54 [1.93–3.34] respectively) (Table 3).