The invention relates to a composition comprising a double-stranded RNA (dsRNA) having two complementary strands, comprising at least one block of poly A and the complementary block of poly U, each strand having a length of between 50 and 200 bases, preferably between 55 and 200 bases, and a pharmaceutically acceptable vehicle, carrier or excipient, for use in a method of treating a cancer expressing a TLR3 receptor.