Appendix cancer for pathologists.
How you grade and name it decides what happens to the patient next.
The pathology report is the single most consequential document in appendiceal cancer. Grade, nomenclature, and margin status decide whether a patient is watched, referred to a peritoneal center, or over-treated on a colorectal pathway. This guide covers the reporting choices that most change outcomes.
Grade in three tiers
Appendiceal mucinous adenocarcinoma is graded G1, G2, or G3. Grade 2 is its own category. Collapsing it into a single high-grade bucket loses the distinction that drives prognosis and the intensity of treatment, and it can push a patient toward more aggressive management than the biology warrants. Keep the three tiers explicit in the report.
Use current nomenclature
Names carry clinical meaning here. Legacy terms like mucinous cystadenoma and cystadenocarcinoma have been retired in favor of the entities below. Precise naming is what routes the case correctly.
LAMN
Low-grade appendiceal mucinous neoplasm. Can spread mucin to the peritoneum despite bland cytology. Note whether mucin or epithelium extends beyond the appendix.
HAMN
High-grade appendiceal mucinous neoplasm. High-grade cytology without infiltrative invasion. Less common, more aggressive.
Mucinous adenocarcinoma
Infiltrative invasion present. Graded G1 to G3, which drives everything downstream.
Goblet cell adenocarcinoma
An amphicrine tumor with its own three-tier grading. Not a neuroendocrine tumor, and not to be labeled carcinoid.
Signet ring cell
A high-grade feature. Call it out explicitly, since it shifts prognosis and management.
Neuroendocrine tumor
Appendiceal NET follows a separate staging and management pathway from the epithelial tumors above.
Report the details the surgeon acts on
Beyond the diagnosis, a few findings change the plan directly. State the margin status, including the appendiceal base and mesoappendix. Distinguish acellular from cellular mucin when mucin is present outside the appendix, because the presence of neoplastic epithelium changes stage and prognosis. Document perforation and any extra-appendiceal mucin or epithelium. These are the variables a peritoneal surgeon uses to plan, and they are easy to omit if the case is signed out as routine.
Flag the cases that need referral
A single line in the report can start the right chain of care. Any LAMN or HAMN, any appendiceal adenocarcinoma or goblet cell adenocarcinoma, and any mucin or epithelium beyond the appendix warrant evaluation at a peritoneal surface malignancy center. When you see these, a note recommending specialist referral helps the treating clinician act before a second, non-therapeutic operation narrows the options.
A note on standards
The reference for management is the 2025 consensus guideline for appendiceal tumors (Godfrey et al., Cancer, 2025), not colorectal protocols. Classification follows current WHO and peritoneal surface oncology conventions. This guide is a practical orientation, not a substitute for the full datasets and reporting standards your practice already uses.
Seeing one of these on a slide?
Point the treating clinician to the referral pathway, and to the standard of care that keeps appendiceal cases off the wrong track.
How to Refer a Patient Standard of Care