## 3 PDT in Veterinary Oncology
### Carcinomas  
Carcinomas are malignant tumors of epithelial and glandular origin arising in several organs, including the skin, breast, stomach, and prostate. Several clinical trials in dogs and cats evaluated the outcomes of PDT in the treatment of squamous cell carcinoma [18; 44; 71; 93]. Hematoporphyrin derivative (HPD) was administered intravenously to 12 cats diagnosed with cutaneous squamous cell carcinoma. The cats that presented small non-infiltrating lesions showed partial and complete responses. However, several side effects were seen, including local oedema, redness, itching, erythema, photosensitization, and alopecia [44]. In a trial including five dog patients with neoplasms of different origins, HPD was activated by a 631 nm argon laser. A total response of 67% was observed at two and nine months [101]. A similar approach was performed to treat a dog with nose squamous cell carcinoma, a dog with adenocarcinoma of the oral cavity, and a dog with gastric mucosa squamous cell carcinoma. The patients presented a complete response at 12 months, a complete response at six months, and a partial response (60/40% reduction), respectively [79]. A dog with esophageal carcinoma was treated with three PDT sessions. Porfimer sodium at 2.7 mg/kg was administered intravenously, 200 J/cm\({}^{3}\) were used in the first session, and 250 J/cm\({}^{3}\) were used in the following sessions. The patient presented progressive anorexia, weight loss, and other signs, being euthanized 278 days after the first treatment [102]. Porfimer sodium-based PDT was performed via electromagnetic navigational bronchoscopy to treat three dogs with lung carcinomas [82]. The treatment was successful, and the side effects were tolerable and manageable. One week after PDT, the involved lung lobes were surgically excised and evaluated histologically, showing necrosis, inflammatory cells, and arterial thrombosis in the PDT-treated tumors [82]. 5-ALA at a concentration of 20% was used topically in 11 cats with superficial squamous cell carcinoma, namely ten nasal planum lesions, two pineal lesions, and one eyelid lesion [86]. In the following study, 5-ALA-based PDT treated 55 cats with superficial nasal planum squamous cell carcinomas [85]. PDT was well-tolerated and effective. A high complete response rate was obtained, with some cases showing partial response and recurrences [85; 86]. In the cohort of 55 animals, 96% responded to therapy, and 85% showed a complete response [85]. Six dogs diagnosed with transitional cell carcinoma of the lower urinary tract were treated with 5-ALA, resulting in neoplasm-free intervals of 4 to 34 weeks in five dogs [95]. More recently, 5-ALA (40 mg/kg)-based PDT was performed using a diode laser or LED in four dogs diagnosed with transitional cell carcinoma or adenocarcinoma. Figure 4: Clinical applications of PDT in veterinary medicine. Created with Biorender.com. noma and one cat with sebaceous gland carcinoma. One of the dogs with adenocarcinoma showed a complete local response; however, the progression of the disease was observed. The other patients showed partial response [71]. A dog diagnosed with transitional cell carcinoma of the prostate was submitted to a 5-ALA-based PDT. During the 24 weeks of follow-up after PDT, the disease proved stable with no relevant changes in the animal's health status. However, 34 weeks after treatment, the dog presented an abrupt increase in hematuria, urinary incontinence, and tensmus. The canine evaluation showed an increase in the tumor size, despite the absence of pulmonary metastases. At week 35, the dog was euthanized for reasons unrelated to the treatment performed [103]. Six dogs diagnosed with prostate carcinoma were treated with 5-ALA-based PDT. The administration was performed into the prostate by injection into the periurethral and subcapsular prostatic tissue. The disease progressed locally, causing urethral stimulation signs and distant metastases. The survival time ranged from 10 to 68 days, negatively compared with other treatment approaches [104].