It belongs to the family of mucin-producing carcinomas of the breast, constituting about 1–4% of total breast cancer and includes the following: mucinous carcinoma, mucinous micropapillary carcinoma, mucinous ductal carcinoma in situ, lobular carcinoma with extracellular mucin, solid papillary carcinoma, mucoepidermoid carcinoma and MCA [32]. The gene discussed is MUC5AC; the disease is mucoepidermoid carcinoma.