Grading and staging mucinous neoplasms of the appendix: a case series and review of the literature

The grading and staging of appendiceal mucinous neoplasms is challenging and fraught with terminology problems, but has critical prognostic and therapeutic implications. We utilized a small case series to examine the grading and staging systems of appendiceal mucinous neoplasms and outline the evidence for the new systems proposed in the upcoming 8th edition of the American Joint Committee on Cancer (AJCC) Staging Manual. We reviewed 33 cases of appendiceal mucinous neoplasms with available clinical follow-up data, 6 of which were widely disseminated in the peritoneum. An additional 4 cases with disseminated peritoneal involvement were also reviewed. A detailed review of the literature was performed with an emphasis on features associated with disease recurrence and correlation of grade with outcome. Recurrence was not seen in 64 low-grade appendiceal mucinous neoplasms (LAMNs) confined to the muscularis propria in our series (n = 21) or in the literature (n = 43). Of cases of LAMN with neoplastic epithelium present beyond the muscularis propria, 64% (57/89) had peritoneal disease at the time of diagnosis or follow-up. A majority of studies of disseminated appendiceal mucinous neoplasms showed significant five-year survival differences using a three-tier grading scheme. Thus, LAMNs confined to the muscularis propria are best considered as in situ tumors, as these are cured with complete excision. A three-tier system has prognostic significance and should be used for grading of disseminated appendiceal mucinous neoplasms. The conclusions of this case series and literature review provide evidence to support the changes proposed in the 8th edition of the AJCC Staging Manual.