INTERSTITIAL AND TRANSURETHRAL PHOTODYNAMIC THERAPY OF THE CANINE PROSTATE USING MESO-TETRA-(M-HYDROXYPHENYL) CHLORIN

Photodynamic therapy (PDT) produces localised necrosis with light afte r prior administration of a photosensitising drug. Although the techni que is promising for small tumours of hollow organs, little work has b een done on solid organs like the prostate. We studied the tissue biod istribution and photodynamic effects of meso-tetra-(m-hydroxyphenyl) c hlorin (mTHPC), a potent second-generation photosensitiser, on normal canine prostate in vivo. Using quantitative fluorescence microscopy, t he highest concentration of mTHPC in the prostate was seen 24-72 hr af ter intravenous administration. For PDT, red light (650 nm) was delive red to the prostate by laser fibres inserted via the transurethral or transperineal route under transrectal ultrasound guidance. PDT lesions up to 40 mm in diameter (using 4 fibre sites) were produced, characte rised by swelling, inflammatory response and extensive glandular destr uction. There was persistent glandular atrophy at 90 days, but no disr uption of the main stroma and no change in the ultimate size or shape of the gland. Urethral damage sometimes caused temporary urinary reten tion, but this resolved by 7 days, and no animal became incontinent. O ccasional small lesions were seen in the rectum, but these healed with out sequelae and there were no fistulae. Since cancer and normal prost ate are likely to respond similarly, PDT has considerable promise for treating cancer confined to the gland as large areas of glandular tiss ue can be necrosed with safe healing. Because the structural integrity of the gland is maintained, PDT is unlikely to be of value in the man agement of benign prostatic hypertrophy. (C) 1996 Wiley-Liss, Inc.