Simple SummaryThe cecal appendix is known to the general population because it is where acute appendicitis develops and it usually needs a surgical intervention for treatment. However, it is also the place of origin of tumors with special behavior. Those tumors are uncommon and generate specific clinical situations, such as the mucocele or the pseudomyxoma peritonei syndrome, which are the subject of much debate regarding definitions and pathologic classification. There is great interest in achieving a common language for these tumors that will allow the sharing of research and treatment results which will improve the existing information and management of our patients.AbstractAppendiceal mucinous neoplasms have been classified differently over time causing confusion when comparing results between working groups in this field and establishing a prognosis of the disease. A historical perspective of the different classification systems of these tumors is essential for the understanding of the evolution of concepts and histopathological definitions that have led up to the present moment. We carried out a systematic review of the pathological classifications of appendiceal mucinous tumors and how they have included the new criteria resulting from clinical and pathological research. The latest classifications by PSOGI and AJCC 8th edition Cancer Staging have made a great effort to incorporate the new pathological descriptions and develop prognostic groups. The introduction of these new classification systems has posed the challenge of verifying how they adapt to our casuistry and which one defines best the prognosis of our patients. We reclassified our series of patients treated for mucinous appendiceal tumors with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy following the PSOGI and the AJCC 8th edition criteria and concluded that both classifications correspond well with the OS and DFS of these patients, with some advantage relative to the PSOGI classification due to a better histopathological description of the different groups.