[Epidemiology of the two types of gastric adenocarcinoma in Iceland according to the Laurén histological classification 1990-2009].

Background: In the mid twentieth century gastric cancer was the most common type of cancer in Iceland. In recent decades, however, the incidence rate of gastric cancer has decreased markedly and currently only represents 2-3% of cancer cases. The Laurén classification system classifies adenocarcinoma into two types, intestinal and diffuse. The main purpose of our study was to describe the epidemiology of the two types of gastric adenocarcinoma in Iceland between the years 1990-2009.

Methods: This is a retrospective cohort study. Information on patients diagnosed with gastric cancer in Iceland between 1990 and 2009 was collected from the population based Cancer Registry. Histological descriptions were reviewed and classified according to the Laurén classification system. The records of patients diagnosed with either having intestinal or diffuse adenocarcinomas were reviewed and epidemiological information gathered.

Results: Between 1990 and 2009, 730 patients were diagnosed with gastric adenocarcinoma in Iceland, 447 had intestinal adenocarcinoma and 168 diffuse adenocarcinoma. Patients diagnosed with diffuse adenocarcinoma were significantly younger at diagnosis than those diagnosed with intestinal adenocarcinoma. The sex ratio for intestinal adenocarcinoma was 2.3:1 (M:F) and 1.1:1 (M:F) for diffuse adenocarcinoma. The incidence of intestinal adenocarcinoma decreased more rapidly than that of diffuse adenocarcinoma during this period (0.92/100,000 vs. 0.12/100,000). Median survival rates of intestinal and diffuse adenocarcinomas were 23.7 and 20.6 months, respectively. The difference in survival was found to be statistically significant. The hazard ratio between the two groups was 1.31 (CI 1.03-1.67), corrected for age, sex, stage, year of diagnosis and surgical outcome (radical, non-radical or no operation).

Conclusion: The overall incidence rate of gastric cancer has decreased dramatically in the past 20 years. However, the reduction is largely limited to the intestinal adenocarcinoma sub-group. We conclude that the Laurén classification predicts prognosis in gastric adenocarcinoma with diffuse adenocarcinoma having worse prognosis.

Key Words: gastric cancer, Laurén classification, survival, incidence. Correspondence: Halla Sif Olafsdottir, hsolafsdottir@gmail.com.