All in vivo procedures were conducted in compliance with the Guide for the Care and Use of Laboratory Animal Resources (1996), U.S. National Research Council, and approved by the local Animal Care and Use Committee. Six- to eight-week-old female homozygous athymic nude mice were purchased from Charles River (NCI-Frederick, Frederick, Maryland). Two-million A431 cells were subcutaneously injected in the right dorsum of each of the mice. Tumors reaching in volume were selected for study. The conjugate of panitumumab (antiEGFR antibody) and IR700 was synthesized as previously reported.2 Briefly, panitumumab (Pan, 1 mg, 6.8 nmol; Amgen, Thousand Oaks, California) was incubated with IR700 (IRDye 700DX NHS ester; , 30.8 nmol, in DMSO; LI-COR Bioscience, Lincoln, Nebraska) in (pH 8.5) at room temperature for 60 min. The mixture (Pan-IR700) was purified with a Sephadex G50 column (PD-10; GE Healthcare, Piscataway, New Jersey). The protein concentration was determined with a Coomassie Plus protein assay kit (Thermo Fisher Scientific Inc., Rockford, Illinois) by measuring the absorption at 595 nm with spectroscopy (8453 Value System; Agilent Technologies, Santa Clara, California). The concentration of IR700 was measured by absorption with spectroscopy and the number of IR700 molecules per panitumumab was adjusted to . One hundred micrograms of Pan-IR700 was intravenously injected via the tail vein of a mouse 24 h before PIT. The A431 tumor was treated with continuous NIR irradiation by a 690-nm laser system (BWF5-690-8-600-0.37; B&W TEK INC., Newark, Delaware) at a power density of for 10 min (). As controls, tumors in tumor bearing mice were irradiated by NIR without Pan-IR700 administration.