Photodynamic therapy combined with carbon dioxide laser for successful treatment of cutaneous squamous cell carcinoma within a long-standing and huge seborrheic keratosis.

Seborrheic keratosis (SK) is a common benign lesion in which malignancies like cutaneous squamous cell carcinoma (cSCC) can arise rarely. We report a case of an 81-year-old man who presented a well-demarcated reddish-brown plaque with central raised coarse nodules on the top of his head. Dermoscopy and reflectance confocal microscopy (RCM) showed the possibility of malignant transformation. cSCC was confirmed by histopathology and immunohistochemistry. Considering the fact of local low-risk cSCC within a large SK lesion, carbon dioxide (CO2) laser was used to treat the SK lesion, and reduce the thickness of local cSCC simultaneously. Three sessions of 5-aminolevulinic acid-mediated photodynamic therapy (ALA-PDT) were performed after CO2 laser. Finally, no atypical cells were found by multi-point biopsy after treatment, and follow-up was continued for one year. Therefore, malignant changes of SK are relatively uncommon, but should be suspected when abnormal appearance or symptoms occurred. ALA-PDT combined with CO2 is a safe, effective, and minimally invasive treatment for cSCC arising from a huge SK.