FIELD : medicine; biochemistry.SUBSTANCE : method is proposed for treating a patient with large intestine cancer or lung cancer, where cancer cells express telomerase and are characterized by excessive activation of telomerase. In the method, a patient is administered a first pharmaceutical composition in an effective amount containing 6-thio-2' -deoxyguanosine and a second pharmaceutical composition in an effective amount containing a telomerase inhibitor, imetelstat sodium. Further, the total amount of the first and second compositions is more effective for reducing the stability of the length of the telomere and inducing the death of cells expressing telomerase than the amount of the first pharmaceutical composition separately or the amount of the second pharmaceutical composition separately.EFFECT : invention makes it possible to stabilize the length of telomeres for 12–16 weeks and does not allow cells to reverse the effect that the drug has on the length of telomeres for at least 2–4 weeks.8 cl, 8 dwg, 2 tbl, 1 ex