ERBB2 and breast cancer: However, stronger interaction between epidemiological factors and polygenic risk scores were observed for HER2‐zero BC than HER2‐low BC among either HR‐positive [odds ratios: 10.71 (7.55–15.17) and 8.84 (6.19–12.62) for the highest risk group compared to the lowest risk group] or HR‐negative BC [7.00 (3.14–15.63) and 5.70 (3.26–9.98)].