Basal cell carcinoma (BCC) is the most common cancer in the general population, accounting for 80% of nonmelanoma skin cancer 1. The most significant etiological factors appear to be genetic predisposition and exposure to ultraviolet radiation. The sun-exposed areas of the head and neck are the most commonly involved sites 2.
One of the key unresolved questions in cancer biology is the identification of cells of origin of cancer 3. Interestingly, the exact cellular origin of BCC is still unknown. Classically, it is thought to arise from the epidermal basal cell layer, although current theories support either a follicular or a interfollicular stem cell origin 4. Anderson-Dockter et al. 5 found that cytokeratin (CK) 17 is strongly expressed histologically throughout BCC lesions. CK 17 expression may not necessarily correlate with the more aggressive behavior.
Keratins are epithelia-specific intermediate filament proteins 6. Around 50 keratin genes have been discovered across the species; they have been classified on the basis of their molecular weights and isoelectric points into two subtypes: type I, the members of which are acidic and have low molecular weights; and type II, the members of which are basic or neutral and have high molecular weights 7. Type I keratin 17 is not present in normal epidermis 6; however, it shows a peculiar localization in human epithelial appendages, including hair follicles, which undergo a growth cycle throughout adult life 8. Therefore, it is considered to be a marker of follicular differentiation 9.
Therefore, elucidation of the exact origin from which BCCs arise by means of CK 17 immunohistochemical staining was the focus of interest in the current research.
Materials and methods
The current study comprised a total of 40 paraffin blocks obtained from the Department of Pathology, Faculty of Medicine, Tanta University. The study was approved by the Research Ethics Committee of Faculty of Medicine, Tanta University. The available clinical data were collected from the pathological reports. The studied cases were divided into the following groups: group I included 20 paraffin blocks of BCC (according to the available variants of BCC); and group II (the control group) included 20 paraffin blocks of normal healthy skin taken from tumor-free surgical margins of the same studied cases of BCC. All specimens were subjected to the following:
- Hematoxylin and eosin (H&E) staining was performed for routine examination and identification of the histopathological features of the studied tumors.
- Immunohistochemical staining was performed for 3-μm sections that were deparaffinized in xylene for 30 min and rehydrated with graded alcohol series. Immunohistochemical staining was performed using the UltraVision Detection Kit (TP-015-HD; Lab Vision, Fremont, California, USA) according to the manufacturer’s protocol. Sections from a case of cervical squamous cell carcinoma served as positive controls. Negative controls were prepared by omission of the primary antibody.
Evaluation and scoring of CK 17 immunostaining was carried out. Positive CK 17 staining was defined as cytoplasmic granular brownish staining. The intensity of immunostaining was ranked on a visual scale of 0–3 as follows: 0=absence of immunostaining; 1=low; 2=moderate; and 3=high expression. The extent of immunostaining was also ranked on a scale of 0–3 as follows: 0=absence of immunostaining; 1=focal or less than 10% of cells; 2=patchy or 11–75% of cells; and 3=diffuse or more than 75% of cells 5.
Statistical analysis was carried out using Statistical Package for Social Sciences (SPSS) software for Windows, version 15 (SPSS Inc., Chicago, Illinois, USA). Quantitative data were represented as mean+SD and qualitative data were represented as number and percentage. Both w2 and Fischer w2 testing were used for intergroup comparisons, and P value less than 0.05 was considered significant.
All studied tumors were located in the head and neck region. The studied BCC cases were divided into three subtypes.
Group IA included 10 patients (50%) with nodular BCC. There were six male and four female patients and, their ages ranged from 45 to 70 years, with a mean age of 56.2±7.28 years. Group IB included six patients (30%) with pigmented BCC. There were four male and two female patients, and their ages ranged from 39 to 65 years, with a mean age of 50.8±9.62 years.
Group IC included four patients (20%) with morpheaform BCC. There were three male and one female patients, and their ages ranged from 61 to 78 years, with a mean age of 68.2±8.18 years.
There was no statistically significant relation between the subtype of the tumor and the age and the sex of the studied cases (Table 1).
As regards the extent and intensity of CK 17 expression in normal healthy skin from tumor-free surgical margins of studied cases, focal highly positive CK 17 expression (grade 3) was detected suprabasally in the infrainfundibulum, sebaceous duct, the outer root sheath below the opening of the sebaceous ducts, and in the companion layer, but the epidermal layer of the skin was negative for CK 17 (Fig. 1).
As regards the extent of CK 17 expression in the histological subtypes of BCC, there was no statistically significant difference as all cases with different subtypes showed diffuse expression.
As regards the intensity of CK 17 expression in the studied BCC cases in the nodular type (Fig. 2), there were eight cases (40%) showing grade 3 and two cases (10%) showing grade 2. In the pigmented type (Fig. 3), there were four cases (20%) showing grade 3 and two cases (10%) showing grade 2. In the morpheaform type (Fig. 4), there were three cases (15%) showing grade 3 and one case (5%) showing grade 2. In this type, CK 17 immunostaining clearly detected individual tumor cells away from the dermal tumor strands that seemed nonmalignant with hematoxylin and eosin staining alone.
There were no significant differences as regards the intensity of CK 17 expression between the different subtypes of BCC (Table 2).
As regards the intensity of CK 17 expression in BCC subtypes based on age of patients, the mean age in patients showed a high expression of 59.06±8.86 and a moderate expression of 50.8±11.45, with no statistically significant difference. Moreover, there was no statistically significant relation between the intensity of CK 17 expression in BCC and sex of patients.
As regards the clinical data of the studied cases, the current study revealed that the male/female ratio of the studied patients was ∼2/1, which is in accordance with that reported in previous studies 10–12. This may be attributed to the more frequent exposure of men to different pathogens or carcinogens such as ultraviolet radiation, which is related to the nature of their outdoor work.
Nodular BCC was the most common subtype in this study, followed by the pigmented type, and lastly the morpheaform type. Similarly, Hussain et al.1 reported that the nodular type was the most common type of all BCCs, followed by the pigmented type. However, Ceilley and Del Rosso 13 reported that nodular and morpheaform types were the most commonly observed ones in the head region.
CK 17 immunohistochemical staining of normal skin of the control group revealed a focal pattern of expression located suprabasally in the infrainfundibulum, sebaceous duct, the outer root sheath below the opening of the sebaceous ducts, and in the companion layer, whereas no expression was detected in the normal epidermis, which is similar to that reported in other studies 13,14 that found the expression of CK 17 in the normal pilosebaceous tract but not in normal epidermis.
All studied BCC cases showed diffuse CK 17 expression, which is in agreement with previous reports 5,14 that reported that all BCCs studied showed diffuse positivity for CK 17. However, Alessi et al.15 found that CK17 sometimes showed a focal pattern of expression in some BCC subtypes.
The intensity of CK 17 expression in the studied BCC cases and the control group ranged from high to moderate expression, which suggests a close relationship between BCC cells and hair follicle epithelial cells. These findings are in accordance with the previous postulations that BCC develops almost exclusively in the skin containing pilosebaceous units, with the face being a favored site, which suggests that these anatomic locations may be home to a greater number of precursor or progenitor tumor cells 16. This study revealed a similar pattern of CK 17 expression between BCC, hair follicles, and the glandular components of the pilosebaceous-apocrine unit, which was also observed by Kurzen et al.17, and this suggests that they originate from the outer root sheath and the pilosebaceous-apocrine unit; this correlates with clinical findings, as this tumor is usually not found in the palmer or plantar area 18.
No statistically significant differences as regards the intensity of CK 17 expression were found between the different BCC subtypes. This indicates that the intensity of CK 17 expression may not necessarily correlate with the more aggressive behavior generally associated with the morpheaform BCC variant. Thus, the studied cases of the morpheaform subtype did not have a correspondingly higher expression of CK 17, which is in accordance with previous studies, which reported that CK 17 was strongly expressed histologically throughout most BCC lesions 5,17.
The pattern of CK 17 expression provided additional evidence to the suggestion that the tumorous differentiation in BCC is toward follicular outer root sheath cells and glandular components of the pilosebaceous-apocrine unit. Moreover, the intensity of CK 17 expression may not necessarily correlate with the more aggressive behavior generally associated with the morpheaform BCC variant. However, CK 17 could be used as a useful marker in the identification and outlining of BCC and it can be used for margin evaluation of Mohs sections.
Conflicts of interest
There are no conflicts of interest.
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