In young pregnant women with breast cancer, the most common type of tumour is invasive ductal carcinoma, which is found in 80–90% of cases and corresponds to a higher prevalence of hormone-receptor (HR)-negative status, human epidermal growth factor receptor 2 (HER2)-positive status, and Ki67-positive status [83,84]. Here, ERBB2 is linked to invasive ductal breast carcinoma.