Immunohistochemical Pattern of CD34 Distribution in Different Types of Basal Cell Carcinoma and in Peritumoral Skin

<i>Background and Objectives</i>: Basal cell carcinoma (BCC) is the most common skin carcinoma, mainly occurring in older individuals. The aim of this study was to document the immunohistochemical distribution of CD34 in different histopathological types of BCC, as well as in the peritumoral and uninvolved skin of biopsy samples. <i>Materials and Methods</i>: Excisional biopsies of skin BCCs were routinely processed into paraffin blocks, and microtome sections were stained immunohistochemically for CD34. <i>Results</i>: A consistent finding in skin samples containing BCC was the absence of CD34 in the following extravascular structures: neoplastic cells, epidermis and its derivatives (except for the cells of the isthmic part of the outer hair follicle sheath), fibroblast-like cells of BCC tumor stroma, as well as in the papillary dermis in the tumor region. Fibroblast-like cells of the tumor stroma were variably CD34 immunopositive only in the nodular type of BCC. In all examined biopsies, part of the dermis adjacent to the BCC tumor mass (juxtatumoral zone) was characterized by pronounced CD34 immunopositivity. In the transitional zone of peritumoral skin and in marginal skin, CD34-positive connective tissue cells were observed in the periadnexal dermis around: sebaceous gland lobules, the secretory coils of eccrine sweat glands, the pilosebaceous canal, as well as in the perimysium of the arrector pili muscle. Fibrocytes of fibrous sheaths encasing the isthmic part of hair follicles were CD34 negative, interposed between highly positive epithelial cells of the outer hair follicle sheath and the fibroblasts of the local reticular dermis. The transitional zone and uninvolved skin contained CD34-positive fibroblast-like cells situated between secondary bundles of reticular dermis, as well as CD34-positive cell processes within these bundles. <i>Conclusions</i>: The observed pattern of CD34 positivity within the examined regions shows a specific distribution, providing insight into the adaptive responses of the skin to the tumoral process.