We identified critical enhancers that are required for the gene expression of two major mucins in human IMA, which may also provide the mechanisms of mucin hypersecretion in other cancers such as gastrointestinal, pancreatic, and breast cancers and chronic lung diseases, including idiopathic pulmonary fibrosis (IPF), cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), and asthma. The gene discussed is MUC5AC; the disease is breast cancer.