Photodynamic therapy (PDT) is widely used in the treatment of human skin tumours, although its use in horses and ponies is novel. PDT utilises a light-sensitive cream which is absorbed by more metabolically active cells, such as tumour cells. After absorption, the cream is activated by a light of a particular wavelength and the cells destroyed.
The great benefit of PDT is its selectivity, destroying tumour cells preferentially without the collateral tissue damage associated with other topical tumour treatments. It may be used alone for more superficial tumours, or in conjunction with laser surgery for more invasive or extensive tumours.