PROBLEM TO BE SOLVED: To provide an agent for preventing and treating cancer, containing a gene-silencing siRNA exhibiting silencing effects on the fascin gene.SOLUTION: The gene-silencing siRNA exhibiting gene-silencing effects on fascin 1 is represented by sequence identification numbers 1 to 3. It is discovered that the gene-silencing siRNA has effects for suppressing the proliferation of cancer cells, and as a result, the pharmaceutical composition containing at least one kind thereof is provided.