Metachronous Schnitzler's Metastasis of Gastric Adenocarcinoma 13 Years After Curative Resection: A Case Report

A 54-year-old man presented with constipation with a six-month duration and a 5 kg weight loss over 10 months. He had undergone a subtotal gastrectomy and chemotherapy for advanced gastric cancer 13 years earlier. A colonoscopy revealed a firm, circular, in-growing mass in the rectum. A computed tomography (CT) scan showed a 3.0×1.2 cm invasive mass near the prostate, abutting the rectal wall and invading the right ureterovesical junction, causing hydroureteronephrosis. A positron emission tomography-CT scan indicated low fluorodeoxyglucose uptake in the rectal or prostate area. The biopsy results showed poorly differentiated carcinoma. An immunohistochemistry study confirmed CK7 positive, CK20 negative, MUC2 negative, and CDX2 focally positive immune phenotype for cancer cells, suggesting a diagnosis of metastatic adenocarcinoma with a gastric origin rather than a prostate and rectal origin.