MUC4 and breast cancer: TNBC: Triple-negative breast cancer, HER2: Human epidermal growth factor receptor 2, NAC: Neoadjuvant chemotherapy, AC: Adriamycin and cyclophosphamide, BRCA: Breast cancer gene, DNA: Deoxyribonucleic acid, IMPC: Invasive micropapillary carcinoma, MUC4: Mucin-4, pCR: Pathological complete response