germ cell tumors predominantly arise in the testes or ovaries , and they also occur in extragonadal regions , including the mediastinum , the retroperitoneum , the sacrococcygeal region and the intracranial region . gastric germ cell tumors , and especially yolk sac tumors , are very rare and only few cases have been reported in the english literature [ 1 - 7 ] ; most of these patients have widespread metastases at the time of diagnosis , so they have poor survival . the treatment of gastric yolk sac tumor is aggressive chemotherapy combined with radiotherapy and surgery . we report here on a 61-year - old man with a yolk sac tumor that presented as early gastric cancer . this is the first report of a case of gastric yolk sac tumor presenting as a localized polypoid mass , and this patient was cured after performing gastrectomy with lymphadenectomy . a 61-year - old man was transferred to the department of internal medicine under the presumptive diagnosis of early gastric cancer , which was found accidentally during a routine medical exam . endoscopic examination showed a round polypoid mass with a reddish surface and a central depression ( 1.00.8 cm ) at the posterior wall of the greater curvature and at the mid body ( fig . 1a ) . a computed tomographic scan of the abdomen and pelvis showed a polypoid mass at the greater curvature of the mid body , but any lymph node enlargement was not found ( fig the level of serum alpha - fetoprotein ( afp ) was elevated to 50 ng / ml , whereas the serum cea and human chorionic gonadotropin levels were within the normal limits . under the diagnosis of early gastric cancer , we performed endoscopic mucosal resection ( emr : strip biopsy method ) . during resection , mass base was found to have fibrotic changes , so we performed piecemeal dissection of the tumor in three pieces . the post - emr pathologic findings confirmed a yolk sac tumor with invasion to the submucosa and the resection margin was positive . the mucosectomy biopsy of the stomach consisted of three fragments and the largest measured 1.21 cm in size . a majority of the tumor showed a lace - like ( reticular ) network of medium - sized cuboidal or flattened malignant cells ( fig . 2a ) and also papillary structures with formation of shiller - duval bodies ( fig . other components of germ cell tumors , such as embryonal carcinomas and choriocarcinomas , were not identified . on the immunohistochemical staining , however , the biopsy after surgery showed no residual tumor and no tumor in the lymph nodes . tumor recurrence was not found on the follow - up endoscopy and computed tomographic scan . primary germ cell tumors , and especially yolk sac tumors , are very rare forms of stomach malignancy and only few cases have been reported in the english literature [ 1 - 7 ] . the germ cells first appear from the primitive streak , the splanchnopleure and the allantoic membrane of the embryo , and they migrate toward the gonadal ridge , but some of these germ cells may remain at ectopic sites . yolk sac tumor of the stomach may arise from migrated germ cells , which is similar to other extragonal germ cell tumors . however , some reports have suggested that the stomach arises from the foregut with all of the cells containing the complete genetic material , and the tumor cells may dedifferentiate to form the yolk sac phenotype . most of the previous reports of yolk sac tumor were the cases that presented with both malignant germ cell tumor and adenocarcinoma , and only 2 cases appeared to be a pure yolk sac tumor , without adenocarcinoma . the prognosis of gastric yolk sac tumor is very poor because many of these patients have widespread metastases at the time of diagnosis ; fortunately in our case , the tumor presented as a small polypoid mass that simulated early gastric cancer without lymph node or distant metastasis . we expected that our case would have a good prognosis since the tumor was completely resected at a rather early stage . histologically , yolk sac tumor has the features of an endodermal sinus tumor , including a reticular pattern ( a clear - cell endoblastic pattern ) with glomerulus - like structures ( schiller - duval bodies ) . also , yolk sac tumor cells produce immunoreactive afp , so the serum afp levels are commonly high , and afp can be demonstrated immunohistochemically within the tumor . our case was pure yolk sac tumor that was composed of a reticular network of cuboidal malignant germ cells with typical schiller - duval bodies , and some of which were focal positive on immunohistochemical staining for afp and alpha1-antitrypsin . the patient had increased serum afp before surgery and this decreased to nearly the normal range after surgery . we report here , for the first time in korea , on a case of gastric yolk sac tumor presenting as early gastric cancer and the patient was cured after gastrectomy with lymphadenectomy . in contrast to the cases previously reported in literature , our case seems to have a good prognosis because of the early diagnosis and curative resection . the serum levels of afp could be a useful marker of the clinical course for patients suffering with gastric yolk sac tumor .
gastric yolk sac tumors are extremely rare and their prognosis is poor ; most patients have widespread metastases at the time of diagnosis . 
 the treatment of gastric yolk sac tumors consists of aggressive chemotherapy combined with radiotherapy and surgery . here , we first report a case of gastric yolk sac tumor presenting as an early gastric cancer that was cured after a gastrectomy with lymphadenectomy .