*2.1.3. Mucinous adenocarcinoma*

The main feature of this subtype is the dominance of extra-cellular mucinous pools—by definition, mucinous adenocarcinoma shows more than 50% extra-cellular mucin (**Figure 2C**). It is not uncommon to see some signet-ring cells scattered in the mucin.


\*MSI, microsatellite instable.

**Table 1.** Classification systems of adenocarcinoma.

#### *2.1.4. Signet-ring cell and other poorly cohesive adenocarcinoma*

Non-cohesive, isolated single tumour cells or carcinoma cells arranged in only small aggregates of few cells (**Figure 2D**).

Signet-ring cell carcinoma is composed of more than 50% signet-ring cells. The classic form of signet-ring cells is usually a single cell and has a central droplet of cytoplasmic mucin (optically clear in HE-staining). The atypical, hyperchromatic nucleus is eccentrically placed. Sometimes signet-ring cells can form lace-like glands.

Malignant Gastric Tumours: The Role of Pathologist in the Diagnosis and for Therapeutic Decisions http://dx.doi.org/10.5772/intechopen.69838 271

**Figure 2.** Four main histological subtypes of gastric adenocarcinoma (WHO): (A) tubular adenocarcinoma, (B) papillary adenocarcinoma, (C) mucinous adenocarcinoma and (D) poorly differentiated non-cohesive adenocarcinoma.

Other variants of poorly cohesive adenocarcinomas include (it is important to recognize that signet-ring cell carcinoma is just one subtype in the group of poorly cohesive adenocarcinoma): single cells with deeply eosinophilic cytoplasm, bizarre nuclei, histiocytic-like or accompanied with prominent lymphatic stroma.
