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Evaluating gastric cancer misclassification: a potential explanation for the rise in cardia cancer incidence
A M Ekström1, L B Signorello, L E Hansson
1Department of Medical Epidemiology, Karolinska Institute, Stockholm, Sweden. Annamia.Ekstrom@mep.ki.se
Insights
Cancer registry data for gastric cardia cancer is unreliable. Accuracy in coding cardia tumors was low, suggesting reported incidence trends may be misleading.
Area of Science:
- Gastroenterology
- Oncology
- Cancer Epidemiology
Background:
- Rising gastric cardia cancer incidence raises concerns.
- Diagnostic coding and definition inconsistencies may impact classification accuracy.
- Limited understanding of cardia cancer misclassification in registries exists.
Purpose of the Study:
- To assess the accuracy of gastric cardia cancer registration in a population-based cancer registry.
- To evaluate the impact of misclassification on observed incidence trends.
- To establish a gold standard for gastric adenocarcinoma subsite classification.
Main Methods:
- A Swedish population-based cohort (1.3 million) with newly diagnosed gastric adenocarcinoma (1989-1994) was used.
- Uniform classification of gastric subsites established a gold standard.
- Cancer registry completeness and accuracy for cardia tumors were assessed against this gold standard.
Main Results:
- The Swedish Cancer Registry demonstrated 98% completeness for gastric adenocarcinomas overall.
- Cardia cancer coding completeness was only 69%, with an 82% positive predictive value.
- No improvement in cardia cancer coding accuracy was observed over time.
Conclusions:
- While overall gastric cancer registration is excellent, cardia tumor accuracy is notably low.
- Estimated true cardia cancer incidence may differ significantly (up to 45% higher or 15% lower) from registry reports.
- Observed increases in gastric cardia cancer incidence should be interpreted with caution due to potential misclassification.
Background:
Reports of dramatic increases in gastric cardia cancer incidence warrant concern. However, the recent introduction of a separate diagnostic code, the lack of a consensus definition of the cardia area, and the accelerating interest in cardia cancer may affect classification practices. Little is known about the magnitude of cardia cancer misclassification in large cancer registries.
Methods:
In a well-defined Swedish population (1.3 million), we uniformly classified all patients with newly diagnosed gastric adenocarcinoma (from 1989 through 1994) with respect to gastric subsite, and we used this patient group as our gold standard. We then evaluated the completeness of the Swedish Cancer Registry in registering gastric adenocarcinomas against this gold standard and, further, assessed the completeness of cardia cancer registration and the rate of falsely included cases to estimate the potential impact on observed incidence trends.
Results:
Our gold standard contained 1337 case subjects with gastric adenocarcinoma. Overall, the Swedish Cancer Registry was 98% complete with regard to gastric adenocarcinomas and had a 4% rate of falsely included cases. The completeness of coding cardia cancer was only 69%, and the positive predictive value for cardia cancer was 82%, with no improvement over time.
Conclusions:
Although overall completeness of gastric cancer registration by the Swedish Cancer Registry was excellent, accuracy in registering cardia tumors was surprisingly low. Our estimates suggest that true cardia cancer incidence could be up to 45% higher or 15% lower than that reported in the Cancer Registry. This margin of error could accommodate the observed increase in cardia cancer in Sweden. Therefore, secular trends in cardia cancer incidence should be interpreted cautiously.