ERBB2 and breast lobular carcinoma: We found that compared with the overall and older breast cancer population, a lower proportion of young adult patients had stage IV cancer, lobular carcinoma, HR−/HER2+ expression, only surgery treatment, and BMI ≥ 24 kg/m2, whereas a higher proportion had surgery combined with adjuvant and neoadjuvant therapy, normal and underweight BMI, current cigarette smoking status, and current casual alcohol drinking status.