Veterinary/zoology session

Photodynamic therapy (PDT) has recently become a widely accepted and routinely used modality in clinical oncotherapy. PDT involves topical or systemic application of a photosensitizer agent, that accumulates in neoplastic tissue, but is rapidly cleared from normal tissue. In the peak phase of accumulation the tumor is illuminated with a visible light of a certain wavelength (650nm). This results in formation of various reactive oxigen species (ROS) causing irreversible damage to, or inducing apoptosis of neoplastic cells, leading to tumor regression

The aim of our study was to elaborate the methodology of PDT for small animal clinical practice. The initial phase of the work involved 13 feline patients, seven with squamous cell carcinoma, and six with sarcoma. Carcinomas were localized on the head, while sarcomas mostly the limbs and the trunk. Each treatment followed the same protocol. Biopsies were obtained prior to PDT treatments, and 1 to 2 weeks post-treatment. Blood samples were taken right before PDT, immediately after PDT, and 1 to 2 weeks after PDT.

PDT was proved to be efficient both for treatment of carcinomas and sarcomas, and is clearly more potent against low grade malignancies as compared to high grade ones.

Average Relapse Free Interval (RFI) was 14.5 ±11.1 weeks (median: 13 w), Overall Survial Time (OST) was 23,8 ± 29,9 weeks (median 12 w). Patients were classified as low and high grade cases. Whereas the RFI of low grade cases was 16 ± 11 weeks (median: 16 w) with 41.9 ± 31 weeks (median 30 w) OST, the RFI of high grade cases was 1.5 ± 1.2 weeks (median: 1 w) with 2.7 ± 1.2 weeks (median 2.5 w) OST.

Photodynamic therapy resulted in local inflammatory reactions. Alterations in haematological parameters were observed in blood samples taken immediately following treatment, while biochemical parameters showed marked changes in samples taken 1 week post-treatment or later.