## 5 Conclusions  
In the last decades, veterinary medicine has reached many milestones in therapeutics; however, cancer remains a therapeutic challenge, compromising patients' quality of life and requiring efforts from owners. Nevertheless, domestic animals are part of the family. Their owners are extremely concerned and demanding about their animals' health and quality of life, always searching for less invasive treatments. The applications of PDT in veterinary oncology cover a variety of neoplasms [10]. However, due to sparse investigations, therapeutic protocols are still under debate, and the use of PDT in veterinary medicine is not yet part of the clinical routine [10; 90]. This contrasts with worldwide regulatory approval for treating various benign and malignant diseases in human medicine [38; 168]. This review presents applications of PDT in the oncological treatment in dogs and cats, highlighting the photodynamic treatment protocols and the main photosensizers (Table 7) used in different types of tumors. Unfortunately, the current evidence arises from highly diverse protocols and studies with small numbers of animals. Carcinomas were included in several small trials performed with up to 12 patients [88], where heterogeneity of PDT protocols regarding PS, light, and DLI led to variable responses from nil to complete, associated with mild to \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline
**Photosensitizer** & **Carcinomas** & \multicolumn{2}{c}{**Mastocytomas**} & \multicolumn{2}{c}{**Sarcomas**} & \multicolumn{2}{c}{**Melanomas**} \\ \hline  & **Dogs** & **Cats** & **Dogs** & **Cats** & **Dogs** & **Cats** & **Dogs** & **Cats** \\ \hline HPD & 8 & 12 & 1 & 1 & 2 & - & 1 & - \\ Porfimer sodium & 4 & - & - & - & 12 & - & - & - \\
5-ALA & 17 & 67 & 1 & - & 3 & 1 & - & - \\ BPD-MA & 10 & - & - & - & 25 & - & - & - \\ PAD-S31 & - & 1 & 2 & - & - & - & - & - \\ Talaborfin sodium & 3 & - & - & - & - & - & - & - \\ EtNBS & 2 & 8 & 2 & - & - & - & 1 & - \\ HPPH & 17 & 55 & - & - & 17 & - & - & - \\ CASPc & - & 36 & 1 & - & 8 & - & - & - \\ mTHPC & - & 72 & - & - & - & - & - & - \\ AO & 52 & - & - & - & - & 37 & - & 1 \\ ZnPcS\({}_{4}\) & 6 & - & 1 & - & 3 & - & 1 & - \\ AlCIPc-nano & - & - & - & - & 8 & - & - & - \\ ICG & - & - & - & - & 10 & 6 & - & - \\ \hline Total & 119 & 251 & 8 & 1 & 88 & 44 & 3 & 1 \\ \hline \hline \end{tabular} Legend: 5-ALA, 5-aminolevulinic acid; AlCIPc-nano, aluminum-chloride-phthalocyanine nanoemulsion; AO, acridine orange; BPD-MA, benzopyyrin derivative monoacid ring A; CASPc, chloro-aluminum sulfonated phthalocyanine; EtNBS, 5-ethylamino-9-diethylaminobenzo(a)phenothiazinium chloride; HPPH, pyroropheorhombic-a-hexyl ether; HPD, hematopoporphyrin derivative; ICG, indocyanine green; mTHPC, meta-(tetra hydroxyphenyl) chlorine; PAD-S31, 13,17-bis [1-carboxopropyl]carbamoylethyl-3-ethoxy-iminoethylidene-7-hydroxy-2,7,12,18-tetramethyl porphyrin sodium; ZnPcS\({}_{4}\), zinc phthalocyanine tetrasulfonate.  
\end{table} 
Table 7: Main photosensitizer used in PDT in veterinary oncology. moderate side effects. Frequently, the disease was stabilized for some weeks [85; 86; 95]. We highlighted a trial of 55 cats [85] where 5-ALA was well-tolerated and provided 85% complete response, and a trial with 51 cats [110] with 62% local control. Studies also pointed to higher energies being associated with better outcomes [114] and larger tumors generally being less responsive [18]. Regarding mastocytomas and melanomas, studies with up to 2 patients using multiple PDT protocols do not allow us to draw any conclusions [79; 84; 96]. Regarding sarcomas, a variety of trials with small numbers of animals were reported; the larger study including only 16 dogs, showing 56% recurrence after HPPH-based PDT [121]. Additionally, a trial showed that AO can be interesting as surgical adjuvant [123]. PDT is effective in different neoplasms of dogs and cats. However, complete remission was sometimes not achieved.