Gastric adenosquamous carcinoma with an apparently pure squamous phenotype on limited biopsy in a patient with HIV: A case report.

Gastric carcinomas with squamous differentiation are exceptionally rare and diagnostically difficult, particularly on limited biopsy material. We report a case of an HIV-positive man in his mid-60s who presented with abdominal pain, melena, and unintentional weight loss. Initial upper endoscopy revealed a large, ulcerated mass involving the gastric fundus and cardia; superficial endoscopic biopsies were non-diagnostic. Endoscopic ultrasound-guided biopsy demonstrated invasive squamous cell carcinoma without a glandular component, and the tumor was staged cT4b cN1 cM0 (clinical Stage IVA, AJCC/UICC eighth edition). The biopsy interpretation was treated as provisional, since sampling of this extent cannot exclude a glandular component. After neoadjuvant FLOT chemotherapy, total gastrectomy with multivisceral resection yielded gastric adenosquamous carcinoma with hepatic metastatic adenocarcinoma, establishing M1 disease and Stage IV. A pure squamous phenotype in a gastric biopsy is therefore not sufficient to diagnose primary gastric squamous cell carcinoma; the distinction rests on the resection specimen. The patient's HIV infection is relevant background rather than a demonstrated cause.