PHOTO DETECTION OF CARCINOMA OF THE COLON IN A RAT MODEL - A PILOT-STUDY

Photodynamic sensitizers are light-absorbing chemicals that cause phot oreactions in biologic systems when exposed to light of the proper wav elength. Dihematoporphyrin ethers (DHE) are the active porphyrin deriv atives most commonly used as a photosensitizer (Photofrin, QLT). DHE a ccumulates in tumor tissue and also fluoresces when light activated. A more reliable and less costly screening method for early detection an d treatment of colon cancer is needed. The present study was designed to induce adenocarcinoma of the colon in rats with 1,2 dimethylhydrazi ne (DMH) and attempt to identify tumors early in their evolution by DH E fluorescence. Forty rats were injected with 20 mg/kg of DMH at weekl y intervals until sacrifice. Photofrin (3 mg/kg) was injected through the tail vein in each prior to sacrifice. Eight colonic specimens cont ained invasive adenocarcinoma, seven of which fluoresced when exposed to a Woods lamp. Carcinoma in situ was identified in two specimens by fluorescence, and one fluorescent specimen contained dysplasia.