Results of clinico-morphological and immunohistochemical studies of 44 cases of carcinosarcoma of the uterus are presented in an attempt to provide pathogenetic rationale for prognosticators of the disease. Immunohistochemical reactions were used to evaluate the expression of genes and mediators p53 and PTEN and cyclooxigenase (COX-2) in cells of mesenchyme and epithelium of tumor to gauge the influence of either component on its biological behavior. All patients were divided into two groups depending on whether they revealed expression of p53, PTEN and cyclooxigenase or not. The end results--overall survival and complete remission duration--were compared in both groups. No dominance of either component of carcinosarcoma was established.