Factor XIIIa-positive dendrocytes present at the periphery and inside epithelial neoplasms are an heterogeneous group of cells. They are subsets of mesenchymal cells, cancer-associated macrophages and antigen-presenting cells. Factor XIIIa, other tissue transglutaminases, alpha 2-macroglobulin and tumour necrosis factor-alpha represent a complex network of mediators influencing tumour progression in the skin. In the present study we searched for the presence of dendrocytes and alpha 2-macroglobulin deposits inside and in the vicinity of cutaneous carcinomas (90 basal cell carcinomas and 46 squamous cell carcinomas) and malignant melanomas (69 primary and 28 metastatic tumours). We also studied the proliferation of the same neoplasms by Ki-67 immunohistochemistry. Dendrocytes were numerous, abutting on and infiltrating most basal cell carcinomas and thin malignant melanomas. In contrast, they were present in only low numbers or even absent in thick primary malignant melanomas and in their metastases. They appeared unmodified around squamous cell carcinomas compared with the surrounding skin. Extracellular deposits of alpha 2-macroglobulin were often found in locations where dermal dendrocytes were numerous. No correlation was found between the Ki-67 indices of carcinomas and the density of peritumoral dendrocytes. In contrast, negative relationships were found between the Ki-67 indices and the number of dendrocytes present inside basal cell carcinomas and thin malignant melanomas. This study has yielded circumstantial evidence to link the density of factor XIIIa-positive dendritic cells and a low proliferative rate of neoplastic cells in basal cell carcinomas and malignant melanomas.

Skin equivalent models are used for a wide variety of pharmacotoxicological trials. The present study was performed to assess morphologically the effect of podophyllotoxin on human bioengineered skin. The untreated model exhibited many resemblances with the parent tissues, although the epidermal differentiation was slightly impaired at the ultrastructural level. The penetration of podophyllotoxin and its biological effects inside the model appeared largely increased compared to the clinical experience with the drug. Acantholysis and cytolytic changes were prominent mimicking the effect of cantharidin. The exaggerated response of many skin equivalents to various compounds shed some doubts on the validity of the model when it is used to show efficacy rather than toxicity. This might apply to claims of efficacy for cosmetic compounds. The effect of cosmetic additives cannot be validated by such approach alone.

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