Ultrastructure of cell surface abnormalities in neoplastic histiocytes.

In an ultrastructural study by transmission and scanning electron microscopy of two cases of malignant histiocytosis and a case of leukaemic reticulum-cell sarcoma, unusual blisters, blebs and worm-like processes were detected on the cell surfaces. The blisters (containing clear fluid) appear to develop by a single-membrane-bound vacuole approaching the cell membrane, and acquiring another membrane on discharging from the cell. The blebs (containing cytoplasm) appear to correspond to the already described phenomenon of zeiosis. The term "vermipodia" is given to the worm-like processes. The underlying factors responsible for these phenomena is not clear, but the exocytosis of the clear blisters resembled that of leukaemic blasts exposed to the action of vinca alkaloids. As two of the cases were being treated with vincristine, it may be that a drug action is implicated. However, it is also possible that these changes may be the morphological expression of some of the changes in the cell surface membrane that occur in malignant transformation.