الفهرس 
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Abstract
Basal cell carcinoma (BCC) is a non-melanocytic skin cancer that arises from basal cells layer of epidermis and its appendages and considered the most common skin cancer in humans. In Egypt, the most common skin cancer is Basal Cell Carcinoma BCCs (77%) was followed by (15%) for Squamous cell carcinomas (SCC), and (8%) for melanomas. The incidence of BCC is rising and represents approximately 70–80% of all skin carcinomas. Epidemiological data indicates that the overall incidence is growing 1–3% annually.
While BCCs can develop early in life both sporadically and with certain genodermatoses, age is an independent risk factor. Incidence rate doubles from 40 to 70 years of age. The incidence for those <40 years age is also increasing. Men are more frequently affected than women (1.5-2:1). BCC is generally a slow-growing tumour for which metastases is rare, occurring in only 0.5 percent or less of cases. Even though this malignancy is rarely fatal, BCC can be highly destructive and disfiguring to local tissues when presentation is delayed, or treatment is inadequate especially that 75-80% of BCCs are located on the head and neck.
There are several clinical subtypes of BCC that may exhibit different patterns of behavior. The clinical types of BCC include nodular, superficial morpheoform, fibroepithelioma of Pinkus infundibulocystic, pigmented and Red dot BCC which is a unique clinical variant of BCC.
UV radiation enhances the development of mutations in several tumour suppressor genes and proto-oncogenes which have been implicated in BCC formation. In about 90 percent of cases, the genetic mutations result in hyperactivation of the hedgehog (HH) protein family. Beyond the HH pathway, the TP53 tumour suppressor gene is also plays role in the pathogenesis of BCC. Stem cells have been hypothesized to be the cells at the origin of cancer as they reside and self-renew in tissues for extended periods of time, increasing their lifetime risk of accumulating the oncogenic mutations required for cancer formation.
CD200 is a highly conserved type-1 membrane glycoprotein that is expressed primarily by normal myeloid cells and human hair follicle bulge KSCs, presumably to protect these cells from immunological attack.
LRIG1 is a trans-membrane protein that interacts with and decreases signaling by ErbB growth factor receptors. LRIG1 is located at and contribute to the interfollicular epidermis and the upper pilosebaceous unit. It controls the stem cell compartment of the interfollicular epidermis by maintaining a quiescent non dividing state.
The aim of this study is to evaluate the role of stem cells in different clinical types of Basal cell carcinoma by studying immune-histochemical expression of stem cell markers CD200&LRIG1 and their relations with the pathogenesis of the disease.
This is a retrospective cohort study included 100 patients diagnosed with BCC in 2015 at Nottingham University Hospitals Trust, UK, based on the availability of tissue in formalin-fixed paraffin-embedded (FFPE) blocks. The patients were followed up for five