**2. Classification of primary gastric carcinomas**

In the past 90 years, there have been some different proposals for classification systems (**Table 1**). Especially in Western countries, the classification of Lauren (from 1965) and the current World Health Organisation (WHO) (from 2010) are accepted and of practical importance.

In general, gastric adenocarcinomas are built of (a) cohesive tumour cells forming tubular or papillary structures or (b) poorly cohesive (and often but not always) single carcinoma cells. It is not uncommon to see different growth pattern in the same tumour (morphology-based tumour heterogeneity).
