Infantile Acute Monocytic Leukemia with Tumor Formation in the Skin Expressing Adhesion Molecules as seen by Electronmicroscopy

We report a case of infantile acute monocytic leukemia associated with solid tumors in the skin. Light microscopy showed that the tumor cells were mainly spindle-shaped and arranged in tandem. Immunohistochemical staining showed that fibronectin was detected in the extracellular matrix (and partially on the surface of tumor cells), integrin α5β1 on the cell surface, and vinculin and actin were detected in the cytoplasm of the tumor cells. Electron microscopy showed that the tumor cells had perpendicular transmembranous fibrils and closely situated collections of cytoplasmic microfilaments beneath the cell membrane suggesting fibronexus-like structures. We conclude that the expression of fibronectin, integrin α5β1, vinculin, cytoplasmic actin and fibronexus-like structure in leukemic cells indicate these cells possess an adhesive function. The mechanism of formation of the extramedullar solid tumors in this patients involved these adhesion molecules of the tumor cells.