Abstract Background: Skin tumors represent 4.78% of primary malignant tumors in Egyptian patients. Among the common skin tumors in Egyptian patients; are invasive keratinocytic/ epidermal tumors, constitutes 78.5% of primary skin tumors. Cancer stem cells (CSCs) are a population of cells responsible for tumor initiation, cancer progression and therapeutic resist-ance in manycancers. The CD133 protein is a transmembrane glycoproteinthat has been considered a putative and important CSC biomarker in various tumors, including gastric, breast, and colon tumors. Nestin is an intermediate filament protein that was described as a marker of neural progenitor cells during development of the central nervous system. In tumors, nestin expression is reported in malignancies of various tissues, and high levels have been correlated with aggressive features in brain tumors, non-small cell lung cancer and breast cancer. Aim of Study: To study the immunohistochemical expres-sion of stem cell markers; CD133 and nestin in some skin tumors, to evaluate the relation of their expression with other histopathologic features and other predictor parameters in these tumors. Material and Methods: The immunohistochemical expres-sion of CD 133 and nestin were assessed in 44 cases of kerat-inocytic/epidermal tumors (20 cases of squamous cell carci-noma, 20 cases of basal cell carcinoma and 4 cases of trichoblastoma), which were collected from the surgical pathology files of the histopathology department, Al-Azhar University Hospitals during the period 2018-2020. Three sections of normal skin were also included in the study to assess for the immunohistochemical expression in normal structures. Results: All cases of normal skin included showed negative immunostaining for nestin and CD133. Except for a limited nestin expression related to hair follicles. Nestin was expressed in 14 out of the 20 cases of squamous cell carcinoma (70.0%) with a statistically significant direct relationship between nestin expression and tumor size (P-value 0.015), and tumor grade (p-value 0.04). Nestin was not expressed in any of the 20 cases of basal cell carcinoma or 4 cases of trichoblastoma examined. CD133 was not expressed in any of squamous cell carcinoma, basal cell carcinoma or trichoblastoma cases examined.
Conclusion: Cancer stem cell markers; nestin and CD133 are not expressed in normal skin with exception of limited nestin expression related to hair follicles, a findings that suggest a role of both markers related more to neoplastic process rather than normal physiological processes. Nestin was expressed in squamous cell carcinoma with statistically significant relationship with tumor size (measured by maximal tumor dimension) and tumor grade. This may explain in part the aggressive behaviour of some high-grade squamous cell carcinoma cases. Nestin was not expressed in basal cell carcinoma; which may indicate different cellular origin and may explain the indulant locally malignant behaviour of such tumors.