Peripheral blood neutrophils of 123 patients in stage Ia of the endometrial cancer have been assayed. The receptor system and ability of neutrophils to form extracellular traps (NET activity) were assessed by fluorescence microscopy, and spontaneous production of IL-2, IFN-γ, matrix metalloproteinase (MMP), G-CSF was found to exist determined with enzyme-linked immunosorbent assay. Phagocytic and myeloperoxidase activity, the level of cationic proteins, and neutrophil activity were evaluated in an NBT test determining the oxygen-dependent bactericidal action of neutrophils. Topology and rigidity of neutrophil membranes were assessed using scanning probe microscopy. It was established that an increased number of neutrophils was accompanied by changes of their receptor system, aerobic and anaerobic cytotoxicity, enhanced phagocytic activity, and reduced NET activity. The secretory activity of neutrophils changed. An increased level of MMP-1, possibly by enhanced production of reactive oxygen species, reduced IL-2 level, and a drastic increase in G-CSF were observed. The architectonics of neutrophils at stage Ia of endometrial cancer was characterized by altered cell shape and granularity loss. The rigidity of the cell membrane decreased. The changes in neutrophil morphology and persistent hyperactivity suggest the existence of the equilibrium between the immune system and the tumor in stage Ia of endometrial cancer.