Abstract: A method to treat solid tumors and other oncological diseases consists of parenterally injecting an agent which destroy's blood's extracellular DNA into the systemic blood circulation of a cancer patient to slow down malignant. The agent is embodied in the form of a DNAse enzyme and, more particularly, as a bovine pancreatic DNAse. Doses from 50,000-250,000,000 Kunz units/day are injected for 5-360 days. A binding agent or an agent that modifies the chemical composition of the blood extracellular DNA is additionally injected into the blood. This modifying agent is preferably an enzyme-ribonuclease.