Design: Interobserver agreement study on whole-slide images
Population: 20 appendiceal goblet cell adenocarcinomas graded by 7 pathologists
Primary outcome: Agreement on WHO 5th edition grade and individual features
Effect: Fleiss kappa 0.29 (95% CI 0.14-0.44); full agreement in 4/20 cases

The WHO 5th edition grades appendiceal goblet cell adenocarcinoma in three tiers. This study, published in June, circulated whole-slide images of 20 tumours to seven pathologists with an interest in appendiceal disease.

All seven agreed on the grade in only 4 of 20 cases. Overall agreement was fair (Fleiss kappa 0.29, 95% CI 0.14-0.44), and pairwise agreement ranged from none to good. Agreement was best for extracellular mucin and tumour sheets (kappa about 0.4) and worst for mild architectural disarray and necrosis (kappa 0.05-0.07).

If experts disagree this much, grade is a weak basis for decisions on further surgery or chemotherapy. The authors suggest a two-tier system may be more reproducible; that has not yet been validated.

In practice, describe the proportion of high-grade patterns alongside the grade, and consider review where grade would change management.

Seven experts agreed on the WHO grade in only 4 of 20 goblet cell adenocarcinomas.
Necrosis and mild architectural disarray were the least reproducible features.
Report the estimated proportion of high-grade patterns alongside the grade.
Seek a second opinion when grade would decide further surgery or chemotherapy.
The WHO system has not changed; a two-tier alternative is a proposal, not a standard.

Why it matters

Clinicians plan right hemicolectomy and chemotherapy partly on this grade.

The statistics, in plain English

A kappa of 0.29 means agreement only modestly better than chance. A kappa near 0.05 for a feature means agreement on it is little better than guessing.