Aim. To determine the cell loss factor in patients with prostate cancer by comparing the values of actual tumor growth rate with its proliferating activity.

Materials and methods. 63 patients diagnosedwith morphologically confirmed prostate cancerwere included into the study. The level ofKi-67 expression in biopsy specimens of prostate adenocarcinomawas evaluated for every patient of the group. The initial prostate-specific antigen (PSA) doubling time was evaluated on the basis of the data concerning the kinetical properties of PSA. The data describing actual tumor growth rate and its proliferating activity was compared to the parameters characterizing the tumor status (incidence, Gleason score and the initial PSA level). Results. Tumor growth rate significantly accelerates in proportion to the increase of tumorincidence and PSA level and also to the decrease in the differentiation of prostate cancer according to the Gleason score.In all casesthis is accompanied by the statistically significant decrease of cell loss.At the same time, Ki-67 proliferation index remains unchanged regardlessthe stage of the disease and the initial PSAlevel. Natural increase in the mitotic activity occurs only as the level of tumor cell differentiation drops.

Conclusion. Prostate cancer growth rate is largely defined by the cell loss factor.?e research on kinetical propertiesin the prostate cancer pathogenesis might explain the nonuniformity of a clinical course (tumors vary from indolent, protractedly non progressive to fulminant),reveal the mechanisms of castrate-resistance and find new ways of drug applications. Further research on the evaluation of the real growth rate of prostate cancer and its proliferating activity is required.

Authors declarelack of the possibleconflicts of interests.