• Infiltrative invasion (desmoplastic reaction, small angulated irregular glands or tumor budding)• Well-differentiated adenocarcinoma: neoplastic epithelium with minor nuclear atypia lining the cystic mucin pools• Poorly differentiated: no or little gland formation• Adenocarcinoma with signet ring cells: <50% signet ring cells present• Signet ring cell carcinoma: >50% signet ring cells present. The gene discussed is MUC5AC; the disease is adenocarcinoma.