Cytomorphology of murine B16 melanoma in vivo after treatment with cyclophosphamide: evidence of "oncotic" cell death.

Cytopathological alterations of transplanted murine B16 melanoma cells were exmmned as a function of time after intraperitoneal injection of cyclophosphamide, and quantitatively compared with tumor growth curves and colony forming ability. Marked swelling of tumor cells, both cytoplasmic and nuclear, was observed in a dose-dependent manner and this preceded tumor volume regression. The swollen cells appeared to constitute a non-clonogenic cell population. The observed cellular swelling may be a typical example of oncosis, a form of accidental cell death, and distinct from apoptosis (programmed cell death). In addition, the existence of another type of cell death was suspected, which might accompany cell shrinkage or lysis, preceding the "oncosis".