Interobserver, intraobserver, and interlaboratory variability in reporting pT4a colon cancer

Area of Science:

• Oncology
• Pathology
• Gastroenterology

Background:

• The pT4 category in colon cancer has increasing clinical significance and therapeutic implications.
• Accurate staging, particularly pT4a, is critical for treatment decisions in colon cancer patients.

Purpose of the Study:

• To evaluate the diagnostic variability of pT4a colon cancer among pathologists and laboratories.
• To assess the impact of this variability on colon cancer staging and potential understaging.

Main Methods:

• Twelve pathologists classified 66 Hematoxylin/Eosin-stained colon cancer slides based on tumor proximity to the peritoneal surface.
• Inter- and intraobserver variability were assessed using Kappa statistics.
• Interlaboratory variability was analyzed using pathology reports from the Dutch Pathology Registry (2012-2015), comparing the proportion of pT4a diagnoses across 33 laboratories.

Main Results:

• Moderate interobserver agreement (Kappa=0.50) and substantial intraobserver agreement (Kappa=0.71) were observed among pathologists.
• A significant interlaboratory variability in pT4a diagnosis was found, with 8 out of 33 laboratories diagnosing pT4a significantly more or less frequently than the median.
• Tumors diagnosed as pT4a had a higher mean number of blocks taken compared to pT3 tumors, suggesting potential differences in pathological assessment.

Conclusions:

• Substantial variability exists in diagnosing pT4a colon cancer at both the pathologist and laboratory levels.
• The assessment of pT4a stage in colon cancer is challenging, highlighting a need for standardized diagnostic criteria and evaluation methods.