Large intestine malignancy is the second most common malignancy and second leading cause of cancer mortality in Poland. This is related to late detection of these lesions, e.g. due to lack of effective screening tests. Lesions found by a surgeon are clinically advanced, making the treatment often ineffective and sometimes even completely impossible. Discovery of a substance that would be able to stop key processes for the development of malignancy could change such situation. Activity of certain enzymes was found to increase in malignant cells and invasion of malignancy could be triggered by inadequate amount of endogenous inhibitors of these enzymes in the surrounding healthy tissues. Inhibitors identical with that produced in human cells were found in egg whites.The aim of the study was to determine ability of cystatin isolated from egg whites to inhibit activity of cathepsin B and L.Material and methods. Immunohistochemistry and histology of tissue specimen collected from malignant lesions resected from 60 patients diagnosed with large intestine adenocarcinoma, who underwent surgical treatment in 2nd Department of General and Oncological Surgery, Medical University of Wrocław between 2007 and 2009.Results. Differences were fund between health tissues, margins and center of the malignant lesions with regard to amount and distribution of stained cathepsin B - cystatin complexes. The above mentioned inhibitors were able to inhibit 90% of primary activity of cathepsin B and L in malignant tissues.Conclusions. Cystatins obtained from egg whites could be used as substances supporting anti-cancer therapy in the future.