The present study used indocyanine green (ICG) and a broadband light source apparatus [photodynamic hyperthermal therapy (PHT) group] in order to treat a colon 26 tumor-bearing mouse model. The other groups were administered either ICG alone (ICG group), light alone (light group) or no treatment (control group). Following the treatment, tumor growth was measured. Nine days after the treatment, the tumors were resected and histological and immunohistological examinations were performed. In the PHT group, the growth rates of the tumor tissues were significantly decreased compared with those observed in the other groups (P<0.05). The proportion of necrotic areas in the PHT and light groups were increased significantly compared with those observed in the ICG and control groups. However, there were no significant differences between the PHT and light groups. The proportion of Ki-67 in the PHT and light groups was less than that observed in the ICG and control groups. The number of terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive cells in the PHT group was significantly increased compared with that observed in the other groups. These data indicate that PHT is effective in vivo and in vitro.

Sixteen cases of malignant soft tissue sarcoma (STS; 10 canines and six felines) were treated with a novel triple therapy that combined photodynamic therapy, hyperthermia using indocyanine green with a broadband light source, and local chemotherapy after surgical tumor resection. This triple therapy was called photodynamic hyperthermal chemotherapy (PHCT). In all cases, the surgical margin was insufficient. In one feline case, PHCT was performed without surgical resection. PHCT was performed over an interval of 1 to 2 weeks and was repeated three to 21 times. No severe side effects, including severe skin burns, necrosis, or skin suture rupture, were observed in any of the animals. No disease recurrence was observed in seven out of 10 (70.0%) dogs and three out of six (50.0%) cats over the follow-up periods ranging from 238 to 1901 days. These results suggest that PHCT decreases the risk of STS recurrence. PHCT should therefore be considered an adjuvant therapy for treating companion animals with STS in veterinary medicine.

The anticancer effects of photodynamic hyperthermal chemotherapy (PHCT), which consists of a combination of indocyanine green photodynamic hyperthermal therapy and local chemotherapy, have previously been reported. The present study investigated the effect of PHCT in six cases of feline vaccine-associated sarcoma (FVAS) following conservative surgical resection. No recurrence was observed in three out of six (50%) cases, while recurrence was observed in the remaining three cases. Of note, each feline with recurrences had previously undergone surgical resection more than three times, whereas those without recurrence had undergone no or one previous resection. In addition, the three animals in which there was no recurrence survived between 893 and 1,797 days following surgery. In conclusion, the results of the present study suggested that PHCT may be a candidate as a novel adjuvant cancer therapy for FVAS.