## 3 PDT in Veterinary Oncology
### Carcinomas
Two cats with a planum nasal lesion showed complete response, and one with a forehead lesion recurred. Therapeutic responses were variable, but no significant systemic toxicity or skin photosensitization were reported [113]. Squamous cell carcinoma lesions in 15 cats were followed up three months after CASPc-based PDT. 3/15 cats had no response, 2/15 cats had a partial response (50% reduction), 10/15 cats had a complete response, and 2/15 cats had a recurrence following a complete initial response [83]. CASPc activated by 100 and 200 J/cm\({}^{2}\) was used to determine whether an increase in fluency would improve the advanced squamous cell carcinoma remission period. Among ten cats, neoplasms subjected to 100 J/cm\({}^{2}\) had an inferior remission period, of 0 to 619 days free of neoplasms, compared to those treated with 200 J/cm\({}^{2}\), which had 151 to 1057 days of remission [114]. Zinc phthalocyanine tetrasulfonate (ZnPcS\({}_{4}\)) was applied to six dogs with squamous cell carcinomas. Irradiation was performed with a diode laser at 100 J/cm\({}^{2}\). PDT was well-tolerated, with no toxicity signs and partial to complete tumor response [84]. A liposomal formulation of meta-(tetra hydroxyyphenyl) chlorine (m-THPC) was investigated in 18 cats with cutaneous squamous cell carcinomas. While mild erythema was observed in 15% of patients, all patients responded completely. Nevertheless, the tumor recurrence rate was 20%, with an average recurrence time of 172.25 (\(\pm\)87.1) days [93]. The same formulation was administered to 38 cats affected by 63 tumors in the head and neck. Patients with invasive tumors progressed in up to six months. The overall response rate was 84% (complete remission in 61% and partial remission in 22%), with an average-free disease interval of 35 months and an average overall survival time of 40 months. Tumor location did not seem to influence response, but larger tumors were less responsive [18]. The liposomal and lipophilic formulation of mTHPC was investigated in fellines with squamous cell carcinomas. The bioavailability in the tumor was 2 to 4 times higher with the liposomal formulation. All cats responded to therapy with both formulations [115]. The vascular effects of PDT in squamous cell carcinomas in cats were investigated with power Doppler ultrasonography. Lipsosomal and lipophilic mTHPC photosensizers were administered intravenously and irradiated with a diode laser (652 nm). During PDT, a significant decrease in vascularity and blood volume was noted. The lowest values were found 24 h after PDT [116]. PDT with the photosensitizer arcidine orange (AO) was used in a pilot study including five dogs with intranasal tumors, namely three adenocarcinomas, one transitional carcinoma, and one undifferentiated carcinoma [117]. Fourteen dogs with intranasal carcinomas were included in the continuity of the study. The photosensizer was administered into the tumor bed through a five-minute placement of a gauze soaked in a solution (1 ug/mL). Irradiation took place with xenon light between 400 and 700 nm. The median progression-free and overall survival time after treatment were 13 and 22 months, respectively [118]. In the retrospective study, the effects of PDT associated with other therapies (surgery, chemotherapy, and radiotherapy) were evaluated in treating intranasal dog tumors. Overall results showed that 54% of dogs presented recurrence and a median interval of disease-free progression of 12 months after AO-PDT. Cases of recurrence were retreated. After re-AO-PDT, dogs presented an overall recurrence median of 27 months, while dogs submitted to hypofractionated radiotherapy presented a median of 14 months. Side effects were mild