A hepatocellular neoplasm accompanied with massive histiocyte infiltration.

This report presents the case of a unique hepatocellular nodule occurring in a 73-year-old Japanese male with diabetes mellitus and mild obesity. The nodule consisted of hepatocyte-like tumor cells and abundant foam cell type histiocytes that filled up a sinusoid-like space and formed central loose fibrosis. The superficial area did not contain as many histiocytes and showed hepatocellular adenoma character, but there was a focal hepatocellular carcinoma-like lesion, thus suggesting hepatocellular adenoma with malignant transformation. The background liver showed an almost normal histology except for mild steatosis with no specific infiltration of macrophages. These macrophages contained abundant fat droplets, whereas the tumor cells had no fat droplets. The expressions of monocyte chemoattractant protein-1 and macrophage colony-stimulating factor were significantly higher in the tumor than in the background liver. These findings suggested such macrophage infiltration induced by the tumor cells and these macrophages probably phagocytosed surplus fat at the intercellular space of this unique tumor.