Advances in the application of photodynamic diagnosis in Skin Tumors.

Photodynamic Diagnosis (PDD) is a non-invasive imaging technique. It relies on a photosensitizer that, when activated by a specific light source, causes metabolically active tissues like tumors to emit visible red fluorescence. PDD offers high sensitivity, high specificity, and real-time visualization. This article reviews advances in the use of PDD for common cutaneous tumors, including Keratinocyte Carcinoma and extramammary Paget disease (EMPD). In managing skin tumors, PDD can be used during preoperative, intraoperative, and postoperative stages. This helps optimize diagnosis and treatment. Preoperatively, PDD clearly delineates tumor margins and identifies subclinical lesions. It aids in planning surgical or photodynamic therapy-especially for multifocal or ill-defined lesions, such as Bowen's disease and actinic keratosis. Intraoperatively, PDD guides surgeons in determining excision boundaries in real-time. This increases the rate of negative margins (for example, up to 98.6% in cutaneous squamous cell carcinoma surgery) while reducing the number of surgical stages and tissue damage. Postoperatively, PDD can evaluate treatment response, monitor for residual disease, or detect early recurrence. This enables non-invasive, repeatable follow-up. Limitations of PDD include false positives due to inflammation, interference from nonspecific fluorescence, limited depth of fluorescence penetration, and variability in tumor tissue. Looking forward, new technologies such as nanotechnology, artificial intelligence, and multimodal imaging may broaden the use of fluorescence detection in dermatology.