A Case of Early Gastric Cancer with Solitary Metastasis to the Pleura
A 76-year-old woman with a 1-month history of epigastric discomfort was referred to the Department of Gastroenterology. She was being treated as an inpatient in the department of neurology after a diagnosis of Parkinson disease. Twenty days previously, she was found to have a gastric ulcer after having undergone upper gastrointestinal endoscopy in a local clinic. She continued to complain of abdominal discomfort, although she had been taking ulcer medications. On admission, her physical examination findings and laboratory data were unremarkable. A small amount of left pleural effusion was noted on a chest radiograph, and an abdominal radiograph showed no abnormality. Because she had upper respiratory symptoms, including cough, on admission, she had received antibiotics for suspected pneumonia. During her hospital course, a few days after starting the antibiotics, she showed improvement in respiratory symptoms. Symptoms associated with Parkinson disease and other upper respiratory symptoms had been well controlled with an oral antiparkinson drug and oral cough syrups followed by 3-day intravenous antibiotics. She did not report any upper respiratory symptoms, so the pleural effusion was expected to disappear soon.\nUpper gastrointestinal endoscopy was performed to evaluate her symptoms. Endoscopic examination demonstrated a slightly elevated lesion (4 cm) with multiple shallow erosions, absence of a definite ulcer scar, and bridging or converging folds over the anterior wall of the antrum (type IIa) (). The endoscopic ultrasonographic (EUS) image revealed that the diffuse thickened hypoechoic lesion was limited to the mucosal layer, with no irregular narrowing or budding sign (). Histopathological examination of gastric biopsies showed a moderately well-differentiated adenocarcinoma. Abdominal computed tomography (CT) revealed no evidence of gastric wall thickening, enlargement of abdominal lymph nodes, or distant metastasis. The lesion was diagnosed as mucosal gastric cancer. She was transferred to our department for ESD, which was performed according to the expanded ESD criteria.\nOn the day after ESD, the patient reported fever and frequent cough. A follow-up chest radiograph showed an increased amount of left pleural effusion (). Aspiration pneumonia was suspected, and a diagnostic thoracostomy was performed along with initiation of intravenous antibiotic therapy.\nThe ESD specimen revealed a round, brownish, elevated lesion measuring 6×4×0.4 cm, with no surface change. Microscopic examination showed that the tumor was limited to the submucosal layer, with no involvement of the deep resection margin. The tumor showed clusters, or nests, of moderately well-differentiated adenocarcinoma, mostly confined to the large, dilated lymphatic channels with adjacent foci of stromal invasion (). The mucosal layer also showed multifocal lymphatic tumor emboli without stromal invasion.\nAnalysis of the left pleural fluid revealed the following findings: red blood cells, 32,000/mm3; white blood cells, 1,120/mm3; neutrophils, 4%; lymphocytes, 38%; adenosine deaminase activity, 15.4; and pH, 7.36. The ratio of pleural fluid protein to serum protein was 0.98. The ratio of pleural fluid lactate dehydrogenase (LDH) to serum LDH was 0.66. Metastatic adenocarcinoma cells were unexpectedly detected by cytological examination of the pleural effusion ().\nTo determine the primary site of metastatic adenocarcinoma, immunohistochemical (IHC) staining tests and positron emission tomography (PET)-CT were performed. EGC metastasis to the pleural space is rarely observed, but the ESD specimen from this patient showed this unusual histopathological feature.\nThe results of IHC staining tests were as follows: D2-40, positive; cytokeratin 7 (CK7), positive; CK20, negative; CD56, negative; synaptophysin, negative; human epidermal growth factor receptor-2, negative; and thyroid transcription factor-1, negative. The test results were negative for mucin (MUC) 1 and MUC2, and positive for MUC5A and MUC6.\nPET-CT showed a focal abnormal hypermetabolic lesion in the aortopulmonary window, most likely representing malignant uptake; the standard uptake value (SUV) was 8.76. The SUV was elevated in the left lower lobe of the lung, with pleural effusion; the SUV of 4.43 indicated probable benign uptake.\nAfter all analyses, instead of gastric metastasis, we concluded that the proper diagnosis was primary EGC metastasis to the pleura, with accompanying unusual histological findings. We planned to start chemotherapy, but she refused further treatment and wanted to undergo conservative management. She died 1 year after the diagnosis.