PHOTODYNAMIC THERAPY OF A TRANSPLANTED PANCREATIC-CANCER MODEL USING META-TETRAHYDROXYPHENYLCHLORIN (MTHPC)

Pancreatic cancer is difficult to treat, even for tumours localized to the pancreas. Photodynamic therapy (PDT) is a non-thermal technique f or producing localized tissue necrosis with light after prior administ ration of a photosensitizing drug and it could have a role in the loca l treatment of these cancers. We studied PDT in a transplanted cancer in the hamster pancreas using the photosensitizer mTHPC (meta-tetrahyd roxyphenylchlorin). Fluorescence microscopy showed maximum levels of m THPC in normal pancreas 2-4 days after sensitization and in tumour at 4-5 days. For PDT, animals were given 0.1 or 0.3 mg kg(-1) mTHPC and t he tumour was treated at laparotomy 2 or 4 days later with red light ( 50 J at 650 nm, continuous or fractionated) delivered via a single fib re touching the tumour surface. The maximum zone of tumour necrosis (s een 3 days after PDT) was 8.7 mm in diameter with continuous irradiati on, increasing to 12.4 mm with light fractionation (four equal fractio ns with 3 min between fractions). The main complication was sealed duo denal perforation, seen in 3 of 16 animals, probably due to inadequate shielding of the duodenum from the light. The duodenal problems seen in hamsters are unlikely to cause trouble in the much thicker human du odenum. PDT tumour necrosis in this animal model has now been shown wi th a range of photosensitizers, but mTHPC is attractive as it is likel y to produce the largest volumes of necrosis around each treatment poi nt with short light exposure times. This technique could have a role i n the treatment of localized cancers of the pancreas in patients unsui table for surgery and can now be considered for preliminary clinical t rials.