MALIGNANT TRANSFORMATION OF NAKAMURA TYPE-IV GASTRIC POLYP WITH CA-19-9 PRODUCTION

In a 68-year-old Japanese man, a gastric polyp 24 mm in diameter with a stalk 15 mm in diameter was diagnosed as well differentiated adenoca rcinoma and treated by endoscopic polypectomy. Histologically, most of the resected tissue was adenoma, and atypical cells were papillarily proliferating to form adenocarcinoma in adenoma, a Nakamura type IV ga stric polyp. Infiltration of carcinoma was limited to within the mucos al layer. Immunohistochemical study with anti-CA19-9 antibody revealed positive staining in carcinoma cells. Serum CA19-9 level, which showe d slight elevation, returned to the normal range 1 month after the pol ypectomy. The proliferating cell nuclear antigen (PCNA) labeling index and DNA ploidy pattern were analyzed in the resected tissue. The PCNA labeling index was 30% in carcinoma, 17% in adenoma, and 0.1% in the normal tissue. The DNA ploidy pattern was diploid in adenoma and aneup loid in adenocarcinoma. These findings suggest that gastric adenoma, a s well as colonic adenoma, may have the potential for malignant transf ormation.