Gastric Involvement by Metastatic Colorectal Adenocarcinoma With Signetring Cell Morphology Presenting at the Margin of a Perforated Lesion: Case Report

Background: Gastric metastasis from colorectal adenocarcinoma is an uncommon event and may pose a significantdiagnostic challenge because metastatic lesions can mimic primary gastric carcinoma morphologically. The diagnosticdifficulty is greater when the metastatic tumor exhibits poorly cohesive or signet-ring cell morphology, which ischaracteristically associated with primary gastric carcinoma. Case Report: A 40-year-old woman with a known diagnosis ofcolorectal adenocarcinoma presented with abdominal pain and was evaluated for suspected gastrointestinal perforation.During surgical management, tissue from the margin of the perforation was submitted for histopathological examinationalong with an appendicectomy specimen. Histological examination of the perforation-margin tissue revealed ulceratedgastric mucosa infiltrated by predominantly discohesive malignant cells arranged singly and in small clusters. The tumorcells showed abundant intracytoplasmic mucin with eccentrically displaced, compressed nuclei, resulting in characteristicsignet-ring morphology. Tumor cells infiltrated the underlying gastric wall and were identified within the muscular layer.Immunohistochemical examination demonstrated tumor-cell positivity for pan-cytokeratin, CK7, CK20 and CDX2. In thecontext of the patient's established colorectal adenocarcinoma and the morphological and immunophenotypic findings, thelesion was interpreted as gastric involvement by metastatic colorectal adenocarcinoma with signet-ring cell morphology. Theaccompanying appendix showed congestion and inflammatory changes without evidence of malignancy. Conclusion:Gastric involvement by colorectal adenocarcinoma is rare and may closely mimic a primary gastric malignancy, particularlywhen signet-ring cell morphology is present. Recognition of metastatic disease requires careful correlation of morphology,immunohistochemistry and the clinical history. The possibility of metastatic colorectal carcinoma should be considered evenwhen malignant cells are unexpectedly identified in tissue obtained from the margin of a perforated gastrointestinal lesion.