Abstract
Gastric adenocarcinoma (GAS) is a rare subtype of mucinous adenocarcinoma characterized by gastric differentiation and is unrelated to human papillomavirus (HPV) infection. This report discusses a 40-year-old female who presented with abdominal distension accompanied by increased abdominal circumference. CT of the abdomen and pelvis showed a large 21.0*12.7*26.0 cm mass later diagnosed as GAS combined with squamous cell carcinoma on surgical pathology. Immunohistological staining of GAS was positive for CK7, MUC6, PAX-8 CEA, and P53 (wild type) and negative for CDX2, CK20, ER, PR, P16, and WT1. The proliferative index (Ki-67) was 20%. Immunohistochemical staining of squamous cell carcinoma was positive for P16 and P53 (wild type), and the proliferative index (Ki-67) was 90%. However, the pathogenesis and molecular mechanisms of GAS have not been fully elucidated. As more cases are identified and reported, additional targeted therapies can be developed and tested in these patients.