ERBB2 and breast cancer: After stratifying by HR‐status, stronger interaction was still observed for HER2‐zero BC than HER2‐low BC among either HR‐positive ([7.55–15.17] and 8.84 [6.19–12.62] for the highest risk groups compared to the lowest risk group) or HR‐negative BC (7.00 [3.14–15.63] and 5.70 [3.26–9.98]) (Figure 5 and Table S9).