Indocyanine green enhanced near‐infrared laser treatment of murine mammary carcinoma

It is well accepted that near‐infrared (NIR) lasers are appropriate to ablate benign lesions and induce irreversible thermal injury in deeply seated blood vessels. At this wavelength, the laser light penetrates deep (3–5 mm) into the skin. However, many researchers have reported noticeable pain, extending from mild to severe, during and immediately after NIR laser treatment. Intravenous administration of an exogenous chromophore [indocyanine green (ICG), dye] can effectively convert NIR laser light into heat. In this approach, the presence of ICG has shown to enhance thermal injury of blood vessels in the treatment of healthy tissues. However, the effectiveness of thermal injury on the regression of cutaneous carcinomas during ICG/NIR laser therapy has not been assessed. The purpose of our study was to evaluate the potential benefit of using ICG/NIR laser therapy to regress superficial carcinoma with thermal injury. Two groups of A/J mice with subcutaneous mammary adenocarcinoma tumors (7–9 mm) were irradiated with a 808‐nm NIR laser preceded by tail vein injection of ICG dye or sterile saline. Histological evaluation of the subcutaneous tissue revealed minor thermal damage and necrosis in the laser/saline group and substantial damage (up to 100% necrosis) in the laser/ICG group. The laser/ICG‐treated group showed a steady reduction in tumor volume compared to the laser/saline group: 48% by day 5 (p = 0.045) and 69–70% by days 8, 9 and 10 (p values 0.0005 or less). The vascular‐targeted ICG–NIR laser therapy appears to have potential for treating superficial tumors.