A 57-year-old woman was referred to our hospital becauseof a liver mass detected by computed tomography.She hadtaken oral contraceptives for only one month at the age ofthirty.Physical examination revealed no abnormalities,andlaboratory data,including hepatic function tests,were withinthe normal range,with the exception of elevated levels ofthose serum proteins induced by the absence of vitamin K orby raised levels of the antagonist (PIVKA)-Ⅱ (3 502 AU/ml).Abdominal ultrasonography revealed a hyperechoic massmeasuring 10×10 cm in the left posterior segment of theliver.Because hepatocellular carcinoma could not becompletely excluded,this mass was resected.The tumorconsisted of sheets of uniform cells with clear cytoplasm,perinuclear eosinophilic granules and round nuclei.Thesehistological findings were consistent with liver cell adenoma.Background hepatic tissue appeared normal.After resectionof the tumor,serum PIVKA-Ⅱ fell to within the normal range.An area of hepatocellular carcinoma (HCC) with a mid-trabecular pattern was immunohistochemically found,whichwas positive for PIVKA-Ⅱ.Sinusoidal endothelial cells wereCD34-positive,containing scattered PIVKA-Ⅱ positive cells.This tumor was therefore finally diagnosed as liver celladenoma with focal malignant transformation to HCC. A 57-year-old woman was referred to our hospital becauseof a liver mass detected by computed tomography. He hadtaken oral contraceptives for only one month at the age of thirty. Physical examination revealed no abnormalities, and laboratory data, including hepatic function tests, were withinthe normal range, with the exception of elevated levels of serum protein presumed by the absence of vitamin K orby raised levels of the antagonist (PIVKA) -II (3 502 AU / ml) .Abdominal ultrasonography revealed a hyperechoic mass effect 10 × 10 cm in the left posterior segment of the liver.Because hepatocellular carcinoma could not be completely eliminated excluded, this mass was resected. tumorconsisted of sheets of uniform cells with clear cytoplasm, perinuclear eosinophilic granules and round nuclei.Thesehistological findings were with liver cell adenoma. background hepatic tissue normal. After resection of the tumor, serum PIVKA-II fell to the normal range. Ann area of ​​hepatocellular carci noma (HCC) with a mid-trabecular pattern was immunohistochemically found, which was positive for PIVKA-II. Inusoidal endothelial cells were CD34-positive, containing scattered PIVKA-II positive cells. This tumor was therefore finally diagnosed as liver celladenoma with focal malignant transformation to HCC.