ERBB2 and breast cancer: Breast cancer was the cancer most frequently diagnosed in the anti-ERBB2 drug group (209 [97.7%]), whereas chronic myeloid leukemia (611 [29.6%]) and BC (476 [23.1%]) were the 2 most frequent types of cancer in the other anticancer drug group (Table 1; eFigure 2 in Supplement 1).