S6392 Beyond Adenocarcinoma: A Rare Case of Primary Gastric Squamous Cell Carcinoma

Introduction: Squamous cell carcinoma (SCC) of the stomach is an exceedingly rare malignancy, with an incidence of less than 0.5% of all gastric cancers. Unlike the squamous epithelium of the esophagus and anal canal, the gastric mucosa consists of glandular epithelium which makes primary gastric SCC a poorly characterized disease. Risk factors are not well established due to insufficient data, but it is most often seen in man patients in the sixth or seventh decade of life. We present a rare case of primary gastric SCC and highlight the important diagnostic and therapeutic considerations. Case Description/Methods: A 78-year-old woman was admitted to the hospital for evaluation of a 3-month history of decreased appetite and weight loss. Her symptoms persisted despite discontinuation of empagliflozin. Initial labs were significant for hemoglobin 7.1 g/dL, which was acutely decreased from 10.2 g/dL 3 months earlier. Computed tomography (CT) thorax/abdomen/pelvis visualized a large, enhancing mass in the gastric fundus. Upper endoscopy showed an ulcerative friable mass in the gastric fundus; colonoscopy was unremarkable. Gastric biopsy pathology demonstrated pleomorphic, atypical tumor cells which were strongly immunoreactive for p40 and CK7, weakly immunoreactive for GATA3, and non-immunoreactive for CK20, PAX8, CD56, SOX10, and CDX2—overall consistent with gastric SCC. Positron emission tomography scan confirmed localized gastric SCC and possible local node involvement; however, there was no evidence of metastatic disease or alternative primary malignancy. Following tumor board discussion, the patient was initiated on a 6-week course of chemoradiation with carboplatin and paclitaxel, followed by surgical resection. Discussion: The Japanese Gastric Cancer Association has proposed diagnostic criteria for primary gastric SCC which requires histologic confirmation with absence of malignant glandular cells, as well as exclusion of the following: esophageal mucosal extension, location in the cardia, and metastatic disease from an alternative SCC site. Timely diagnosis with upper endoscopy and gastric biopsy is essential to establish a more accurate prognosis. There is no standardized chemotherapeutic regimen currently for primary gastric SCC due to its rarity; however, surgical resection offers the best long-term survival in cases without advanced metastatic disease. Individualized, multidisciplinary care is essential to optimize health outcomes in the absence of clinical guidelines.