ERBB2 and breast cancer: Factors affecting the rate of incomplete radiation treatment include Charlson‐Deyo comorbidity index (13.6% for score 0, 12.6% for score 1, 23.8% for score 2, p < 0.001), osseous location (8.9% for appendicular vs. 16.1% for axial, p < 0.001), dose per fraction (0% for 8 Gy, 3.8% for 4 Gy, 24.6% for 3 Gy, 38.0% for 2.5 Gy and 12.5% for 2 Gy, p < 0.001), and breast cancer subtype (12.7% for LA, 14.4% for LB, 18.8% for TN, and 18.3% for HER2, p = 0.007).