The paper presents data on the intestinal microbiota of cancer patients against the background of invasion by unicellular protozoa Blastocystis spp. A high level of infection (more than 64%) with blastocysts in persons with oncological diseases of the digestive system was revealed. It is known that the intestinal microbiota was formed during the evolution of human society and is individual for each organism. Analysis of the data obtained during the experiment showed an imbalance of the intestines in the examined individuals, expressed in a sharp decrease in the obligate (indigenous) flora and a significant increase in the colonization resistance of the number of opportunistic groups of microorganisms, which can cause chronic inflammation of the intestine, with characteristic clinical manifestations. The dependence of the severity of the degree of dysbiotic disorders and blastocyst invasion was established. In persons with blastocyst invasion, the most pronounced imbalance in the structure of the established intestinal microbiome, which in the future can serve as a platform for the development of various intestinal diseases. For a long stay in the host organism and participation in the formation of a special parasitocenosis Blastocystis spp. morphophysiological properties are required that allow the protozoa to participate in the creation of an individual intestinal community of the examined individuals. These properties include persistence factors that allow organisms to create their own microbiocenosis in cohabitation with other microorganisms in the studied biotope. In this work, using the example of anti-interferon activity, the persistence of blastocysts was studied, which allows them not only to participate in the formation of a special intestinal parasitocenosis, but also to carry out symbiotic relationships among microbes in the intestines of cancer patients.