ADJUVANT INTRAOPERATIVE PHOTODYNAMIC THERAPY DIMINISHES THE RATE OF LOCAL RECURRENCE IN A RAT MAMMARY-TUMOR MODEL

The use of photodynamic therapy (PDT) as an adjunct to curative tumour resection was investigated in a tumour recurrence model, using rat ma mmary adenocarcinoma BN472. Tumours were inoculated subcutaneously in 60 animals and resected after 21 days of growth. Immediately after rem oval, the operation site was exposed to 320-450 nm light of 0.1 W cm(- 2) and 60 J cm(-2) after photosensitisation with either Photofrin (5 m g kg(-1) i.v. 48 h before illumination) or 5-aminolaevulinic acid (ALA ) (2 mg ml(-1) in drinking water for 9 days). Porphyrin concentrations were measured in tissue samples. After 28 days, animals treated with adjunctive PDT had a significantly longer tumour-free interval than co ntrols (P < 0.01); median 25 days (Photofrin), 18 days (ALA), 14 days (controls). Moreover, in the PDT groups significantly fewer rats had l ymph node metastasis. A porphyrin concentration ratio between tumour a nd mammary tissue of 2:1 was found after Photofrin and 4:1 after ALA. The results indicate that adjuvant intraoperative PDT may be a safe an d effective method of destroying residual tumour, thereby preventing l ocoregional tumour recurrence.