5-Ethylamino-9-diethylaminobenzo[a]phenothiazinium
chloride (
EtNBS) is a novel
photodynamic therapy (
PDT)
photosensitizer with efficacy against experimental murine
tumors. In this preliminary study, dogs and cats with naturally occurring
tumors were treated with
EtNBS-
PDT to determine safety and efficacy. Fifteen treatments were performed on 13 animals (9 treatments in 8 cats and 6 treatments in 5 dogs), generally using 400 J of 652 nm light. Two feline sublingual
squamous cell carcinomas (SCCs) responded briefly (minor response). Six feline facial SCCs were treated, resulting in two partial responses and four long-term complete responses (CR). Two canine intraoral SCCs were treated; one responded minimally for 2 weeks (minor response), and one achieved long-term CR. One canine cutaneous mast cell
tumor achieved CR, and one canine ocular mast cell
tumor responded briefly. One canine ocular
melanoma did not respond to treatment. Systemic reactions included
nausea associated with
photosensitizer injection in two cats and two dogs, elevated body temperatures during treatment in two dogs, elevated body temperature 2 days after
PDT in one cat, and inappetance for 2 weeks in one cat. A
peripheral neuropathy of undetermined cause occurred in one cat 2 weeks after
PDT and resolved without treatment. Local reaction was well tolerated in 13 of 15 treatments. All animals were exposed to normal daylight after less than 5 days (mean, 3.5 days) without residual
photosensitization.
EtNBS-
PDT is safe for dogs and cats and has activity against selected naturally occurring
tumors, with an overall objective response rate (partial response + CR) of 61.5%.