Photodynamic therapy response in cats with cutaneous squamous cell carcinoma as a function of fluence

The response of advanced stage cutaneous squamous cell carcinomas (SCC) following treatment with photodynamic therapy (PDT) has been poor. It was the aim of this pilot study to determine whether an increase in the delivered fluence (i.e. energy density) would improve the duration of tumour remission in cats with advanced-stage SCC. Tumours were treated with aluminium phthalocyanine tetrasulphonate (AlPcS₄ ) PDT at a fluence of either 100 J cm^-2 or 200 J cm^-2 and tumour response was evaluated at regular intervals. Those feline tumours treated with a fluence of 100 J cm^-2 (n= 8) had a significantly shorter median remission duration (69 days; range 0-619 days) than those feline tumours treated with 200 J cm^-2 (n= 6; 522 days; range 151-1057 days). It is our conclusion that a fluence of 200 J cm^-2 is well tolerated and more effective when treating cats with advanced stage cutaneous SCC.