To provide a marker for determining sensitivity of a patient to an anti-cancer agent, and novel cancer therapeutic means employing the marker.The marker for determining sensitivity to an anti-cancer agent is formed of a protein selected from the group consisting of a protein or a fragment thereof which is detected as a peak at m/z of 16,450 to 16,620, a protein or a fragment thereof which is detected as a peak at m/z of 22,080 to 22,310, and a protein or a fragment thereof which is detected as a peak at m/z of 17,100 to 17,270, the peaks being determined by means of a mass spectrometer.
