Radiotherapy resulted in similar ten-year ipsilateral recurrence rates in HER2-positive (11.0%) and HER2-negative (9.6%) DCIS patients, whereas omission of radiotherapy resulted in much higher ten-year ipsilateral recurrence rates in HER2-positive (42.1%) than HER2-negative (17.5%) DCIS patients, mainly due to a substantial increase in in situ recurrences [12]. This evidence concerns the gene ERBB2 and ductal breast carcinoma in situ.