According to the most recently endorsed classification of tumors, established by the World Health Organization (WHO), this is a poorly cohesive (discohesive) gastric carcinoma. It is a diffuse, poorly differentiated carcinoma, also known as “linitis plastica.” The term’s etymology involves “linitis” meaning inflammatory change and “plastica” meaning not pliable, with an appearance similar to its often-used moniker “leather bottle ” stomach (Image 6).
Classification of gastric adenocarcinomas based on the WHO (2010) criteria includes the following categories: tubular, papillary, mucinous, poorly cohesive (signet ring carcinoma and other variants) and mixed carcinoma. Although WHO classification is recommended for clinical use, it is not required. Lauren Classification may be used in conjunction with the WHO categories. Based on the Lauren classification, tumors are separated into diffuse, intestinal, mixed and indeterminate types. Diffuse type carcinoma, such as the presented case, consists of poorly cohesive cells with little or no gland formation, infiltrating predominantly or exclusively as isolated malignant cells. Diffuse type gastric carcinoma appears to arise from the mid layer of the mucosa (as noted in the resection micrographs A-B, Image 5) and is not typically associated with intestinal metaplasia. Submucosal fibrosis is commonly present. In deeply invasive tumors, hypertrophic muscularis propria, with desmoplastic stroma, and perineural invasion are common (desmoplastic stroma is evident in the resection micrograph C, Image 5, the black arrow further indicates perineural invasion). Signet ring carcinoma (ring-like due to intracellular mucin displacing the nucleus) is one of the variants of diffuse type, others are histiocytic, plasmacytoid or mononuclear in appearance. Being epithelial, in comparison to lymphoproliferative malignancies, diffuse type gastric carcinomas are positive with keratins (as noted in our biopsy Image 3 B, malignant cells are highlighted by Keratin (AE1/AE3, Biocare), see the blue arrow). Signet ring cells, containing intracellular mucin, will stain with mucicarmine and/or Alcian blue-PAS. Regardless of the variant, diffuse type/poorly cohesive gastric carcinoma is considered high grade.
Are the morphologic features and positive keratin staining sufficient to diagnose diffuse type gastric carcinoma in our case?