Interstitial photoradiation therapy for primary solid tumors in pet cats and dogs.

Photoradiation therapy, a new method for treatment of solid malignant tumors, depends upon the tumor localization and retention of hematoporphyrin derivative, which is activated in vivo by light in the red region of the spectrum. As currently applied to cutaneous and s.c. lesions, the light dose is limited by both normal tissue reactions and the effective penetration of the light through the tissues. In this report, primary solid malignant lesions in pet cats and dogs have been treated by interstitial photoradiation therapy by applying the activating light from a laser [635 +/- 5 (S. D.) nm] directly into the tumor masses thrugh a 200-micrometer quartz fiber optic. Twelve of 14 lesions (four osteosarcomas, two squamous cell carcinomas, two malignant melanomas, one mast cell sarcoma, one fibrosarcoma, one sebaceous gland sarcoma, and a metastatic prostatic carcinoma) responded to treatment, and three are currently considered permanently controlled at 1 year or more following treatment. This method has not only allowed photoradiation therapy to be applied to some remote lesions but has also nearly eliminated normal tissue effects, thus greatly extending the applicability of this treatment to a wide range of human tumors.