胃MALTリンパ腫の経過観察中に発見された急速進行性胃癌の1例

Rapid Growing Gastric Cancer Diagnosed During Follow-up of Gastric Mucosa-associated Lymphoid Tissue (MALT) Lymphoma

要旨　患者は60歳，男性．2000年6月に検診目的で行った上部消化管内視鏡検査(EGD)にて，胃mucosa-associated lymphoid tissue(以下，MALT)リンパ腫と診断された．Helicobacter pylori(Hp)陰性であったが，Hp除菌療法によりMALTリンパ腫は改善し，その後定期的に経過観察されていた．2004年5月に施行したEGDでは明らかな異常はなかったが，1年5か月後のEGDで胃角部～体中部小彎に大きな潰瘍性病変を認め，当初悪性リンパ腫を疑ったが，生検で低分化腺癌と診断された．胃全摘術を行い，大きさ80×75mmの3型胃癌，病理組織学的にpor 1，深達度SS，N1と診断された．免疫組織染色で増殖能のマーカーであるKi-67がびまん性に強陽性で，vimentinとAE1/AE3がいずれも陽性を示した．

　A 60-year-old man was referred to Shinshu University Hospital in June 2000, for further examination and treatment of a gastric neoplasm. He underwent an esophagogastroduodenoscopy (EGD), and histological findings of the biopsy specimens obtained from the whitish gastric mucosa in the lesser curvature of the lower body revealed infiltrations of atypical lymphoid cells and lymphoepitherial lesions. Immunohistochemical studies strongly suggested low grade MALT lymphoma of the stomach. Helicobacter pylori (Hp) infection was not detected although atrophic change of the gastric mucosa and intestinal metaplasia were recognized, suggesting past infection of Hp. At first, he received eradication therapy against Hp and, consequently, infiltrations of atypical lymphoid cells were shown to have regressed remarkably. After that, the patient was followed up at regular intervals including EGD, with no further treatment. EGD showed no abnormal finding in the stomach except atrophic change in May, 2004, but a large tumor with central ulceration was detected in the lesser curvature of the middle portion of the stomach in October, 2005. Judging from endoscopic findings, we considered the possibility that MALT lymphoma might transform into diffuse large B-cell lymphoma. However, histological findings of biopsy specimens showed poorly differentiated adenocarcinomas that were diffusely positive for immunostaining using Ki-67. He underwent total gastrectomy, and the tumor size was 80×75 mm. Histopathological diagnosis was as follows;por 1, pT2 (SS), int, INFβ, ly3, v2, p0, pDM (－), pN1. Immunohistochemical study showed that carcinoma cells were positive for not only cytokeratin but also vimentin. This finding revealed that this cancer had both phenotypes of epithelial cells and non epithelial cells, and was characterized by very undifferentiated cells. He died of recurrence of gastric cancer in June, 2006.