Appendiceal Carcinoma Grading
Separate nonmucinous and mucinous grading, with independent appendiceal and peritoneal assessment.
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Educational and decision-support tool only. Does not replace the current CAP protocol, AJCC/WHO classification edition in use, or professional pathologist judgment — particularly regarding discordant appendiceal/peritoneal grading and the pseudosignet-ring cell distinction.
Reference
Scope
Two independent grading schemes, selected by tumor type. Nonmucinous carcinoma is graded by percentage gland formation; mucinous neoplasms are graded by cytologic atypia and signet-ring status, with the appendiceal primary and any peritoneal disease assessed independently.
Not applicable to poorly differentiated neuroendocrine carcinoma or goblet cell adenocarcinoma. Although rigorous grading criteria have not been formally validated for appendiceal carcinoma, histologic grade has been shown to be a prognostic factor across several published series.
Nonmucinous — full criteria
| Grade | Differentiation | Criterion |
|---|---|---|
| G1 | Well-differentiated | >95% gland formation |
| G2 | Moderately differentiated | 50–95% gland formation |
| G3 | Poorly differentiated | <50% gland formation |
Mucinous — full criteria (AJCC, modified from Davison et al.)
Graded by cytologic atypia, tumor cellularity, and signet-ring cell status — never by percentage gland formation.
Independent assessment: the appendiceal (primary) tumor and peritoneal disease are graded independently. They are concordant in most instances but can be discordant — when discordant, the final grade for staging is based on the peritoneal metastasis.
| Grade | Criteria |
|---|---|
| G1 | Low-grade cytologic atypia, no signet-ring cells. For peritoneal involvement: acellular mucin or low cellularity (typically <20%) and lacks infiltrative invasion of the peritoneum or other organs. |
| G2 | Mix of low- and high-grade cytologic atypia, or diffuse high-grade cytologic atypia; no signet-ring cells. |
| G3 | High-grade cytologic atypia, usually with a signet-ring cell component. Pseudosignet-ring cells (degenerate cells resembling signet-ring cells, floating in mucin) do not qualify. |
LAMN / HAMN correlation (reference only — not computed from)
Appendiceal mucinous neoplasms with only pushing borders are represented by LAMN and HAMN, corresponding to G1 and G2 respectively.
| Grade | Typical correlate |
|---|---|
| G1 | Typically represented by LAMN (low-grade appendiceal mucinous neoplasm), with or without peritoneal involvement. |
| G2 | Typically represented by HAMN (high-grade appendiceal mucinous neoplasm), with or without peritoneal involvement, or by mucinous adenocarcinoma with destructive invasion and desmoplasia. Often shows complex architecture (cribriform glandular spaces, complex papillary structures). With extra-appendiceal spread: invasion with desmoplasia in the peritoneum, or small mucin pools with numerous strips/buds/tumor clusters; perineural and lymphovascular invasion may be present. |
| G3 | High-grade, invasive, usually with a signet-ring cell component (>10%). By convention, signet-ring cell carcinomas are grade 3 — either pure signet-ring cell adenocarcinoma or high-grade goblet cell adenocarcinoma (can be difficult to distinguish in some cases). |
Grade 4 / undifferentiated — edition discrepancy
Tumors with no differentiation (undifferentiated carcinomas) are categorized as Grade 4 in the WHO 2010 classification, but G4 is not included in the AJCC 9th edition. This tool does not offer G4 as a selectable output — an undifferentiated finding instead produces a note asking you to specify which classification edition is in use.
Sources
Davison JM, et al. — original proposal underlying the AJCC 3-tier mucinous grading scheme.
AJCC Cancer Staging Manual, 9th edition — 3-tier grading scheme for mucinous appendiceal tumors involving the peritoneum (modified from Davison et al.); does not include a G4 tier.
WHO Classification of Tumours — 2010 edition (digestive system tumours) — includes a Grade 4 (undifferentiated carcinoma) category not carried into AJCC 9th edition.
College of American Pathologists (CAP). Protocol for the Examination of Specimens From Patients With Carcinoma of the Appendix (document Appendix_5.1.0.0.REL_CAPCP).