Treatment method

A treatment method for killing a tumor cell, the method comprising:

• administering an antibody-photosensitive substance into a vein;
• inserting an elongated tube in a lumen of an endoscope from a mouth, a nose, or an anus and bringing the elongated tube and the endoscope to a vicinity of a tumor having the tumor cell reachable from the mouth, the nose, or the anus after the administering of the antibody-photosensitive substance into the vein;
• placing an optical fiber into the tumor or in the vicinity of the tumor via a lumen of the elongated tube;
• irradiating at least one of the tumor, the vicinity of the tumor, or a regional lymph node with a first near-infrared ray by the optical fiber;
• and
• irradiating the antibody-photosensitive substance bound to a tumor cell membrane in the tumor cell with a second near-infrared ray after the irradiating of the at least one of the tumor, the vicinity of the tumor, or the regional lymph node with the first near-infrared ray, the second near-infrared ray having a shorter wavelength than that of the first near-infrared ray.