British Journal of Dermatology 2001; 144: 567±574. Bowen's disease, solar keratoses and superficial basal cell carcinomas treated by photodynamic therapy using a large-field incoherent light source S.VARMA, H.WILSON, H.A.KURWA,* B.GAMBLES, C.CHARMAN,² A.D.PEARSE,³ D.TAYLOR§ AND A.V.ANSTEY Department of Dermatology, University Hospital of Wales, Heath Park, Cardiff CF14 4XW, U.K. *Department of Dermatology, St John's Institute of Dermatology, London, U.K. ²Department of Dermatology, Queens Medical Centre, Nottingham, U.K. ³University of Wales College of Medicine, U.K. §Gloucestershire Royal Hospital, Gloucester, U.K. Accepted for publication 18 October 2000 Summary Background Photodynamic therapy (PDT) has not yet been demonstrated to be superior to conventional treatment in the treatment of superficial skin cancers and premalignant skin conditions. A limitation for PDT is the absence to date of a light source suitable for the treatment of larger lesions or `field changes' where several lesions are present on one anatomical site. Objectives To investigate the safety and efficacy of a large field light source, the Waldmann PDT 1200, in the treatment of Bowen's disease (BD), superficial basal cell carcinomas (BCCs) and solar keratoses (SKs). Methods After application of 5-aminolaevulinic acid for 4±6 h, each lesion was irradiated with 105 J cm 22 of incoherent red light centred on 640 nm. Eighty-eight patients with 239 lesions were recruited. Results Within two treatments, 88% of BD lesions, 95% of BCCs and 99% of SKs showed complete clinical clearance. At 12 months the complete response rates were 69% for BD, 82% for BCC and 72% for SK. Conclusions This study confirms that PDT is a useful treatment and that selected superficial BCCs and SKs respond well to PDT. The PDT 1200 light source proved capable of treating multiple lesions amounting to a `field change' and also lesions up to 10 cm in diameter within an acceptable treatment time. Thus far, PDT has failed to become established as a routine treatment for small premalignant and malignant skin lesions as it has not proved superior to simple cheaper conventional therapies such as cryotherapy, curettage and cautery, topical chemotherapy with 5-fluorouracil, or surgery. However, PDT has become established as a treatment for selected cases in some centres. This study suggests a role for PDT in the treatment of large premalignancies, superficial BCCs and field change where existing treatments may be problematic. Key words: basal cell carcinomas, Bowen's disease, incoherent light source, photodynamic therapy, solar keratoses Photodynamic therapy (PDT) involves the activation of a photosensitizer by visible light to create cytotoxic oxygen species and free radicals, which selectively destroy rapidly proliferating cells. 1,2 A variety of premalignant and malignant skin conditions, including superficial basal cell carcinomas (BCCs), 3±8 solar keratoses (SKs) 5,8,9 and squamous cell carcinoma in situ [Bowen's disease (BD)] 6±8,10 has been effectively treated by PDT with a topically applied photosensitizer. After three decades of basic and clinical research 11,12 PDT is gaining popularity as a skin cancer treatment. In some Scandinavian countries it is considered to be the routine first-line treatment for some premalignant and malignant skin diseases. However, as yet, no q 2001 British Association of Dermatologists 567 Correspondence: Dr Sandeep Varma. E-mail: varma@doctors.org.uk