Pathologic changes after photodynamic therapy for basal cell carcinoma and Bowen disease: A histologic and immunohistochemical investigation

Objective: To investigate the in vivo reactions and themechanisms of cell death after photodynamic therapy(PDT) for cutaneous carcinomas. Photodynamic therapyis a new treatment modality for nonmelanoma skin cancers.Its effects on target tissue have been well investigatedin vitro, where apoptosis appears to be the maineffector mechanism, but its effects remain undefined invivo.Design: Skin biopsy specimens were obtained sequentiallyafter PDT for basal cell carcinoma and in situ squamouscell carcinoma (Bowen disease). Evidence from routinehistologic evaluation was compared with a panel ofapoptosis-related (TUNEL [terminal deoxynucleotidyltransferase-mediated biotin–deoxyuridine triphosphatenick-end labeling], caspase-3, and Bcl-2) and inflammatory(CD4, CD8, CD20, CD68, and CD56) markers. Weused electron microscopy to evaluate cell damage at theultrastructural level.Main Outcome Measures: Evidence of the mechanismsof tumor cell damage after PDT, detection of histologicand/or immunohistochemical signs of apoptosis,and time course of the tumor destruction andinflammatory reaction.Results: Early epidermal damage and an acute dermalinflammatory response were detected 15 minutes afterPDT. In basal cell carcinoma, nodule damage progressedfrom scant apoptotic cells seen at the dermalepithelialjunction to massive destruction seen after 1 and2 days. The periphery of the basaloid nodules consistentlyshowed earlier and predominant damage, as demonstratedby the perfect coincidence of histologic and immunohistochemicalevidence with apoptotic markers(TUNEL and caspase-3 staining). Fibrosis and lentigolikechanges were seen in late biopsy specimens.Conclusions: This study defines the time course and characteristicsof the skin tumor response to PDT. Taken together,our observations suggest that direct damage tocancer cells is the main effector mechanism leading toPDT response. The involvement of apoptosis is demonstratedby the simultaneous appearance of histologic, immunohistochemical,and ultrastructural markers that occurin the early phases of the cutaneous reaction to PDT.These observations could help to develop future refinementsof the PDT technique.