ERBB2 and breast cancer: Since most of the patients were irradiated during the period when 2D RT was the standard technique in our institution and three-dimensional (3D) RT was just being introduced, the findings of our study should be verified in a group of patients with early HER2-positive breast cancer treated with modern irradiation techniques such as 3D RT, Intensity-Modulated Radiation Therapy (IMRT) or Volumetric Modulated Arc Therapy (VMAT).