**2.1. WHO classification**

**1. Introduction**

following factors:

• Treatment options

• Dignity

268 Gastric Cancer

• Grading

Normal epithelia

Host factors and acquired

Environmental factors

molecular events

The pathologist who deals with gastric tumours is responsible for the determination of the

• Consider differential diagnosis (main differential diagnosis of gastric adenocarcinoma include neuroendocrine carcinoma, malignant lymphoma, metastasis of lobular breast carci-

• Treatment relevant biomarkers: Her2/neu in gastric adenocarcinoma or in gastrointestinal

Adenocarcinoma (including different subtypes) is the most common malignant gastric tumours of epithelial origin. In Western countries, declining incidence of gastric carcinoma is found; nevertheless, it remains the second most common cause of cancer-related death in the world [3]. In Germany, we expect about 9200 men and 6400 women with a newly diagnosed gastric carcinoma per year, and 70% of them will die carcinoma-related in the following 5

> Telomere reduction

Genetic instability

Atrophic gastritis

Reactive oxygen species

Telomerase activation

Mutations: APC, TP53, KRAS

Intestinal metaplasia

> ErbB2 cation

Adenocarcinoma

Cyclin E overexpression

MLH methylation

Intraepithelial neoplasia

• Morphology-based subtyping of gastric carcinoma (according to WHO or Lauren)

• Main tumour differentiation (e.g. epithelial, mesenchymal, lymphatic)

noma, epithelioid angiosarcoma or malignant melanoma)

stromal tumour (GIST), mutational analysis of c-kit or PDGFR)

• Staging (according to TNM-classification)

• Regression scores after neoadjuvant treatment

Chronic gastritis

mation

**Figure 1.** Pathogenesis of intestinal-type gastric adenocarcinoma.

Noxen

Hp infection

Gene polymorphism

• Surgery resection status (R0-R2)

The current WHO classification system describes four main subtypes of gastric adenocarcinoma and some rare entities [3].
