ERBB2 and neoplasm: There were no statistical differences in baseline characteristics between the 4 groups (ages 18-25, 26-30, 31-35, and 36-40 years), including tumor stage (P=.53), nodal stage (P=.65), clinical stage (P=.33), ER status (P=.42), PR status (P=.16), HER-2 status (P=.89), pathological grade (P=.07), and molecular subtype (P=.43).