ERBB2 and breast cancer: For patients with HER2-positive and HER2-negative breast cancers, the training set consisted of 613 lesions (128 HER2-positive and 485 HER2-negative), the internal validation set comprised 263 lesions (41 HER2-positive and 222 HER2-negative), and the external validation set included 154 lesions (Figure 1).