bcl-2 expression reliably distinguishes trichoepitheliomas from basal cell carcinomas

TRPS1: A Marker of Follicular Differentiation

The trichorhinophalangeal syndrome type 1 (TRPS1) immunohistochemical (IHC) stain has increased in use in recent years as a marker for breast carcinomas. The TRPS1 gene is involved in various tissues, including the growth and differentiation of hair follicles. This article seeks to evaluate the IHC expression of TRPS1 in cutaneous neoplasms with follicular differentiation, such as trichoblastoma (TB), trichoepithelioma (TE), and basal cell carcinoma (BCC). IHC studies were performed on 13 TBs, 15 TEs, and 15 BCCs with an antibody against TRPS1. The study found a variable staining expression of TRPS1 in the tumor nests of TB, TE, and BCC. BCCs were distinct in that none of the BCCs demonstrated intermediate or high positivity, while TBs and TEs showed intermediate-to-high positivity in 5/13 (38%) and 3/15 (20%) of cases, respectively. We observed a distinct staining pattern among the mesenchymal cells of TB and TE. We found that TRPS1 highlighted perifollicular mesenchymal cells adjacent to the nests of TB and TE tumor cells. This staining pattern was absent in BCCs, where only scattered stromal cells were positive for TRPS1. Papillary mesenchymal bodies were also highlighted by TRPS1 in TB and TE. TRPS1 stained various parts of the normal hair follicle, including the nuclei of cells in the germinal matrix, outer root sheaths, and hair papillae. TRPS1 may be a useful IHC marker for follicular differentiation.

Differentiation of Basal Cell Carcinoma and Trichoepithelioma: An Immunohistochemical Study

ABSTRACT

Basal cell carcinoma (BCC) is the most common malignancy of the skin. It is an epithelial neoplasm with origin in the precursor cells of the interfollicular epidermis. Even though it has low metastatic potential, delay in management may lead to local destruction and morbidity. In contrast, trichoepithelioma (TE) is a benign tumor originating from the outer root sheath of the hair follicle. Similar to BCC, TE tends to affect the head and neck region. Both neoplasms may exhibit clinical and histopathological similarities, making them prone to misdiagnosis. Multiple immunomarkers have been used to distinguish among these entities, but so far, no single agent or combination of agents appear to be neither sensitive nor specific enough to differentiate between them. This study was divided into 2 parts. First, 17 cases of BCC and 14 cases of TE were stained with androgen receptor and bcl-2. Then, 27 cases of borderline/equivocal of BCC and 13 cases of borderline/equivocal TE were stained with the same protocol. Sensitivity and specificity were calculated for each individual immunomarker and for the combination of them. Androgen receptor positivity was 100% specific for BCC and borderline/equivocal BCC, whereas bcl-2 diffuse staining pattern demonstrated a sensitivity of 82.4% for BCC and 88.9% borderline/equivocal BCC. When both immunomarkers were combined, the sensitivity for BCC decreased (70.6%) but the specificity remained high (100%). Similarly, the sensitivity for borderline/equivocal BCC was 55.6%, whereas the specificity was 100%. Although moderately sensitive, combining both immunomarkers showed an excellent specificity to discriminate between BCC and TE.

Clinical, Histopathological, and Management Challenges of Multiple Familial Trichoepithelioma: A Case Report of a Patient Presenting with Multiple Facial Papules

Trichoepitheliomas (TE) are benign skin tumours of the pilosebaceous apocrine unit with follicular differentiation. Multiple familial trichoepithelioma (MFT) is a considerably rare condition inherited in an autosomal dominant pattern. We present a case of a 15-year-old male who presented with multiple papulo-nodular lesions in the central face and a family history of a similar type of lesions from his mother. Significance of consideration of various clinical differential diagnoses with serious pathological outcomes, strategies followed in the diagnosis including histopathological evaluation aided by immunohistochemical investigations, and subsequent challenges that may be faced in the management of MFT in light of the presentation with multiple facial papules are documented in this case report.

Desmoplastic trichilemmoma of the scalp: case report and literature review of immunohistochemical staining features

Desmoplastic trichilemmoma (DT) of the scalp is a rare disease. In this report, we describe a 67-year-old man who had a small papule lesion around the hairline of the left scalp for more than 40 years. The lesion had rapidly grown to become a solitary, round, 15-mm neoplasm within 6 months. Histopathological examination showed that the mass was composed of a peripheral layer of columnar cells with nuclear palisading resembling the outer root sheath; the mass was surrounded by a thickened glassy basement membrane. The stroma in the center of the mass displayed solid, hyaline degeneration and an eosinophilic pattern, streaked with epithelial cords or islands. Immunohistochemical evaluation showed diastase-resistant, periodic acid–Schiff-positive desmoplastic stroma at the center, and Ber-EP4-negative tumor cells (CD34-positive focally and Bcl-2-positive at the periphery). The tumor was completely resected, and no recurrence occurred during the follow-up period. In this report, we also summarize immunohistochemical features from previous reports of DT, facilitating differential diagnosis of DT from some invasive skin tumors.

Histologic Mimics of Basal Cell Carcinoma

CONTEXT

- Basal cell carcinoma (BCC) is the most common human malignant neoplasm and is a frequently encountered diagnosis in dermatopathology. Although BCC may be locally destructive, it rarely metastasizes. Many diagnostic entities display morphologic and immunophenotypic overlap with BCC, including nonneoplastic processes, such as follicular induction over dermatofibroma; benign follicular tumors, such as trichoblastoma, trichoepithelioma, or basaloid follicular hamartoma; and malignant tumors, such as sebaceous carcinoma or Merkel cell carcinoma. Thus, misdiagnosis has significant potential to result in overtreatment or undertreatment.

OBJECTIVE

- To review key features distinguishing BCC from histologic mimics, including current evidence regarding immunohistochemical markers useful for that distinction.

DATA SOURCES

- Review of pertinent literature on BCC immunohistochemistry and differential diagnosis.

CONCLUSIONS

- In most cases, BCC can be reliably diagnosed by histopathologic features. Immunohistochemistry may provide useful ancillary data in certain cases. Awareness of potential mimics is critical to avoid misdiagnosis and resulting inappropriate management.

A Case of Trichogerminoma With Pilomatrical Differentiation and a Unique Immunohistochemical Profile

Trichogerminomas are rare adnexal neoplasms first described by Sau et al in 1992. Including the initial report, 20 cases have been reported, all with similar histological features, namely tumor nodules composed of basaloid cells that form densely packed, round nests or "cell balls" and which demonstrate variable degrees of pilosebaceous differentiation. In this study, the authors report a case of a trichogerminoma with pilomatrical differentiation and a unique immunohistochemical profile. The patient is a 71-year-old man with a well-delineated nodule on the top of the scalp. Histologically, the lesion measured 16 mm in greatest dimension and was composed of nodules of basaloid cells with central, compact, slightly eosinophilic cells nests. Immunohistochemically, the tumor nodules diffusely expressed cytokeratins 34βE12, AE1/3, and CK5/6. Diffuse expression of β-catenin and nuclear expression of p63 were also evident. The peripheral basaloid cells, but not the cell balls, expressed CD10, Ber-EP4, BCL-2, and CK7, the latter a previously unreported finding. The histological findings and immunohistochemical profile are compatible with a diagnosis of a trichogerminoma.

A Case of Basal Cell Carcinoma with Outer Hair Follicle Sheath Differentiation

A 70-year-old Japanese man presented at our hospital with an asymptomatic, blackish, irregularly shaped plaque with a gray nodule in the periphery on his left lower leg. The lesion had been present for 10 years and had recently enlarged, associated with bleeding. Histopathologically, the tumor consisted of three distinct parts: The first part showed massive aggregation of basophilic basaloid cells with peripheral palisading and abundant melanin granules, and was diagnosed as solid-type basal cell carcinoma. The second part showed aggregation of clear cells with squamous eddies, and was diagnosed as proliferating trichilemmal tumor. The third part showed reticular aggregation of basaloid cells with infundibular cysts in the papillary dermis, and was diagnosed as infundibulocystic basal cell carcinoma. We diagnosed this tumor as basal cell carcinoma with various forms of hair follicle differentiation, including differentiation into the outer root sheath.

Significance of androgen receptor and CD10 expression in cutaneous basal cell carcinoma and trichoepithelioma

Differential diagnosis of trichoepithelioma (TE) and basal cell carcinoma (BCC) on the basis of clinical symptoms and laboratory investigations may be difficult in certain patients. The aim of the present study was to compare cluster of differentiation 10 (CD10) and androgen receptor (AR) expression patterns in BCC and TE, to investigate the predictive power of these proteins as markers of the two conditions. A total of 39 cases of BCC and 15 cases of TE were retrieved from the pathology department archives. AR and CD10 immunohistochemistry was performed on all of the specimens; 23 BCC cases displayed focal nuclear AR staining, however, none of the cases demonstrated diffuse nuclear staining and 16 BCC cases were negative for AR staining. Stromal CD10 staining was more common in TE cases than in BCC cases, and peripheral CD10 staining was more common in BCC cases than in TE cases. AR immunostaining of the BCC samples typically appeared as scattered clusters and individual cells. In addition, AR and CD10 staining exhibited varying staining intensities within each samples. Incisional punch biopsy specimens have the potential to present false-negative results. Therefore, AR and CD10 staining of total excision biopsies provides a more accurate differential diagnosis of BCC and TE for cases with difficulties in the histopathological analysis.

Multiple Familial Trichoepithelioma with an Adjacent Basal Cell Carcinoma, Transformation or Collision - A Case Report and Review of Literature

Trichoepithelioma is a benign tumor of follicular origin that presents as small, skin-colored papules predominantly on the face. When more than one family member is affected, the disease is known as multiple familial trichoepithelioma (MFT). It is a rare autosomal dominant skin disease. Malignant transformation is very rare. We describe here a case that developed malignant neoplasm in a setting of multiple trichoepithelioma.

Emerging drugs and combination strategies for basal cell carcinoma

INTRODUCTION

Basal cell carcinoma (BCC) is a malignancy that is driven by an activated Hedgehog (Hh) pathway. Smoothened inhibitors are a new promising treatment option for patients with locally advanced or metastatic BCC or basal cell nevus syndrome. But long-term data are still limited, the optimal treatment duration is not yet defined and there are already documented cases with acquired resistance.

AREAS COVERED

Treatment modalities with Hh inhibitors, side effects and potential pharmacological combination options are discussed. The current literature, including PubMed, Cochrane database and registered trials on ClinicalTrials.gov, was searched.

EXPERT OPINION

BCCs typically regress during therapy with Hh inhibitors. Muscle toxicity, dysgeusia and hair loss can be considered as on target adverse reactions. Muscle toxicity is the dose-limiting toxicity of sonidegib. It was not seen with vismodegib because of its high binding to plasma protein α-1-acid glycoprotein. Sonidegib is different and shows a clear dose-toxicity relationship, which allows to address the question of whether there is a dose dependency of regression rate, cure rate and progression-free survival. In addition, basic research has offered strategies to enhance efficacy by the combination with other molecules, such as EGFR inhibitors, MEK inhibitors or immunotherapy.

The rate and pattern of bcl-2 and cytokeratin 15 expression in trichoepithelioma and nodular Basal cell carcinoma: a comparative study

Context:

Histopathological evaluations can differentiate between clinically resembling trichoepithelioma (TE) and basal cell carcinoma (BCC) unless the biopsy specimens are small or superficial. Previous studies used immunohistochemical evaluation for Bcl-2 and cytokeratin 15 (CK15), in attempts to differentiate between these two entities, with heterogeneous findings.

Aims:

This study intended to compare the rate and patterns of Bcl-2 and CK15 expressions between specimens of TE and nodular BCC.

Settings and Design:

Case-series including formalin-fixed, paraffin-embedded cutaneous biopsies.

Subjects and Methods:

Twenty-two BCC and 12 TE specimens were stained for Bcl-2 and CK15 and examined microscopically. The rate and patterns of expressions were compared between the two groups.

Statistical Analysis Used:

Statistical analysis was performed using the statistical software (SPSS version 16.0; SPSS Inc., Chicago, IL, USA), Pearson Chi-square, or Fisher's exact tests, wherever appropriate.

Results:

The two groups were comparable for the expression rate and patterns of Bcl-2 (86.4%: 5 central, 14 diffuse in BCC vs. 83.3%: 2 central, 8 diffuse in TE; P = 0.59 and 0.54 for rate and pattern, respectively). The rate of CK15 expression was significantly higher in TE specimens (66.7%: 4 central, 3 diffuse, 1 peripheral vs. 4.5%: 1 central; P < 0.001). The positive likelihood ratio in distinguishing the two neoplasms was 14.7 (95% confidence interval: 2.1-103.7).

Conclusions:

CK15 but not Bcl-2 staining may help in differentiating between BCC and TE even in BCCs with follicular differentiation.

Diagnostic utility of immunohistochemistry in distinguishing trichoepithelioma and basal cell carcinoma: evaluation using tissue microarray samples

Trichoepithelioma is a benign neoplasm that shares both clinical and histological features with basal cell carcinoma. It is important to distinguish these neoplasms because they require different clinical behavior and therapeutic planning. Many studies have addressed the use of immunohistochemistry to improve the differential diagnosis of these tumors. These studies present conflicting results when addressing the same markers, probably owing to the small number of basaloid tumors that comprised their studies, which generally did not exceed 50 cases. We built a tissue microarray with 162 trichoepithelioma and 328 basal cell carcinoma biopsies and tested a panel of immune markers composed of CD34, CD10, epithelial membrane antigen, Bcl-2, cytokeratins 15 and 20 and D2-40. The results were analyzed using multiple linear and logistic regression models. This analysis revealed a model that could differentiate trichoepithelioma from basal cell carcinoma in 36% of the cases. The panel of immunohistochemical markers required to differentiate between these tumors was composed of CD10, cytokeratin 15, cytokeratin 20 and D2-40. The results obtained in this work were generated from a large number of biopsies and resulted in the confirmation of overlapping epithelial and stromal immunohistochemical profiles from these basaloid tumors. The results also corroborate the point of view that trichoepithelioma and basal cell carcinoma tumors represent two different points in the differentiation of a single cell type. Despite the use of panels of immune markers, histopathological criteria associated with clinical data certainly remain the best guideline for the differential diagnosis of trichoepithelioma and basal cell carcinoma.

Fibroblast-activation protein: a single marker that confidently differentiates morpheaform/infiltrative basal cell carcinoma from desmoplastic trichoepithelioma

Microscopically, differentiating desmoplastic trichoepithelioma from morpheaform/infiltrative basal cell carcinoma can be difficult as both show 'islands and strands of basaloid cells embedded in a sclerotic stroma'. A superficial shave biopsy further compounds the diagnostic conundrum. Although a plethora of immunohistochemical markers have been touted as being of use as adjunct histologic tools, none thus far appears to be consistent and reliable in terms of specificity and/or sensitivity. Fibroblast-activation protein, a type II membrane-bound glycoprotein belonging to the serine protease family, is expressed in the granulation tissue of healing wounds. More recently, it has been identified as a marker of reactive tumor stromal fibroblasts, as it is reportedly selectively expressed in peritumoral stromal fibroblasts of multiple epithelial cancers including cutaneous malignancies such as basal cell carcinoma. Given this, we sought to ascertain the use of fibroblast-activation protein in distinguishing morpheaform/infiltrative basal cell carcinoma from desmoplastic trichoepithelioma. Immunohistochemical staining for fibroblast-activation protein was performed on desmoplastic trichoepithelioma (n=25) and morpheaform/infiltrative basal cell carcinoma (n=25), with the control group comprising scars from reexcision specimens (n=10). As expected, fibroblast-activation protein expression was observed in stromal fibroblasts of all control cases (10 of 10, 100%). Of interest, fibroblast-activation protein expression was observed in peritumoral fibroblasts of all cases of morpheaform/infiltrative basal cell carcinoma (25 of 25, 100%) but not in any cases of desmoplastic trichoepithelioma (0 of 25, 0%). A gradient of fibroblast-activation protein expression was observed in morpheaform/infiltrative basal cell carcinoma with more intense expression noted in fibroblasts abutting the tumor cells, a less intense expression in the distal peritumoral stromal portion, and minimal to loss of expression in adjacent normal tissue. In summary, findings from this study underscore the use of fibroblast-activation protein as a histologic adjunct in confidently differentiating morpheaform/infiltrative basal cell carcinoma from desmoplastic trichoepithelioma.

Bcl-2 and CD10 expression in the differential diagnosis of trichoblastoma, basal cell carcinoma, and basal cell carcinoma with follicular differentiation

BACKGROUND

Both trichoblastoma and basal cell carcinoma (BCC) of the skin are characterized morphologically by the proliferation of basaloid cells; however, BCCs are clinically associated with a more aggressive behavior. An accurate diagnosis of these lesions is essential for effective, timely treatment and appropriate therapeutic decisions.

METHODS

This study includes 40 lesions. Bcl-2 and CD10 immunohistochemistry were performed in all cases and the patterns of expression were analyzed.

RESULTS

Bcl-2 is useful for the detection of BCC with diffuse expression in nests of basaloid cells, but cannot distinguish between BCC with follicular differentiation and trichoblastoma, as both lesions show the same pattern with positive and negative areas. Conversely, CD10 expression can distinguish between trichoblastomas with peritumoral stromal staining and BCCs with epithelial staining. If both stromal and epithelial areas are stained, these cases are classified as BCC with follicular differentiation.

CONCLUSIONS

CD10 is useful for distinguishing between BCC with widespread follicular differentiation and trichoblastomas.

Basal cell carcinomas arising within multiple trichoepitheliomas

Although trichoepitheliomas (TEs) are commonly regarded as benign tumors of follicular origin, the natural history of multiple familial trichoepitheliomas (MFT) and their risk for malignancy has been unclear. We describe a 57-year-old male with numerous skin-colored firm papules and plaques present on the central face since 6 years of age. Recently, some lesions had enlarged and ulcerated. Other family members were similarly affected. Biopsies from multiple lesions showed TEs both alone and associated with basal cell carcinoma (BCC) in the same section, suggesting the secondary development of BCCs within TEs. Many prior reports of BCCs arising within TEs in patients with presumed MFT were likely misdiagnosed cases of nevoid BCC. This report is a compelling example of MFT in which BCCs evolved secondarily. Awareness of the potential for the evolution of carcinoma in patients with MFT is important in the management of these patients.

Merkel cell-poor trichoblastoma with basal cell carcinoma-like foci

We reexamined 11 cases of trichoblastoma, and two cases of trichoblastoma with basal cell carcinoma (BCC)-like foci were found. In these two trichoblastomas with BCC-like foci, the BCC-like foci were often localized in peripheral or deep areas of lesions extending out of the fibrocytic stroma. Immunohistochemistry was performed in five conventional trichoblastomas and in two trichoblastomas with BCC-like foci, using antibodies against CK20 and CK15. No CK20-positive Merkel cells and no expression of CK15 were seen in any neoplastic aggregations of the two trichoblastomas with BCC-like foci. In contrast, increased numbers of Merkel cells and positive staining for CK15 were observed in all five trichoblastomas without BCC-like foci. The five trichoblastomas without BCC-like foci included two trichoblastomas with a popped out or shelled out appearance, which characteristically had a thick fibrous capsule surrounding the fibrotic stroma, demonstrating numerous Merkel cells in the aggregations. Some trichoblastomas may undergo mutations, resulting in the development of foci of BCC and in the loss of the expression of CK15 as well as the disappearance of Merkel cells.

CD10 expression in trichoepithelioma and basal cell carcinoma

BACKGROUND

Trichoepithelioma (TE) is a benign neoplasm that shares both clinical and histologic features with basal cell carcinoma (BCC). However, it is important to distinguish these neoplasms. Limited immunohistochemical stains are available to separate these two tumors.

METHODS

CD10 protein immunohistochemistry was performed on paraffin-embedded biopsies of 13 TE and 23 BCC diagnosed by routine microscopy. Cases were analyzed for pattern of CD10 expression by tumor cells and surrounding stroma.

RESULTS

Twelve of 13 (92%) TE showed positive stromal immunoreactivity. Of these, eight cases also demonstrated positivity of the papilla, and two also showed positivity of the basaloid cells. No TE demonstrated epithelial expression alone. On the other hand, expression of CD10 by basaloid cells was identified in 20 (87%) cases of BCC. Stromal positivity was also identified in three cases of BCC. Condensation of CD10-positive stromal cells around basaloid nests was statistically significant in differentiating TE from BCC (p < 0.0001). Conversely, CD10-positive basaloid cells were seen predominantly in BCC (p < 0.0001).

CONCLUSIONS

This study demonstrates a statistically significant difference in CD10 staining pattern between TE and BCC. Thus, CD10 may be a useful adjunct marker in distinguishing these tumors.

Basal cell carcinoma: biology, morphology and clinical implications

Basal cell carcinoma (BCC) is the most common malignant neoplasm of humans. Rising dramatically in incidence in North America, as likely reflects changing habits of the population and a move from more northerly climes to the sunbelt of the Southern and Southwestern United States, the incidence is surely to rise even higher in the future. The last decade has seen significant advances in our understanding of BCC biology and novel approaches to therapy, which hinge upon accurate diagnosis and subclassification by pathologists. The purpose of this review article is to summate the research advances in our understanding of BCC biology and to acquaint pathologists and clinicians to the practical issues in BCC diagnosis and subclassification which flow there from.

Proliferation, apoptosis, and survivin expression in keratinocytic neoplasms and hyperplasias

The dysregulation of apoptosis occurs in many cutaneous disease states. Several apoptosis inhibitors have been shown elevated in neoplasms and in some inflammatory conditions, but their relation to proliferative and apoptotic states has not been defined. We examined the expression of the apoptosis inhibitor survivin in a panel of keratinocytic neoplasms and hyperproliferative skin lesions using both immunohistochemistry and a newly developed in situ hybridization technique. Proliferation and apoptotic indices were also assessed by immunohistochemical staining for proliferating cell nuclear antigen and TUNEL, respectively. We found the highest rate of proliferation in verrucae and psoriasis followed by actinic keratosis, squamous and basal cell carcinoma, lichen simplex chronicus, and seborrheic keratosis; all were significantly (P < 0.05) higher than normal skin. Apoptotic rate was increased in squamous (P = 0.05) and basal cell carcinoma (P = 0.03), but not significantly different from normal skin in the other lesions tested. Survivin expression was seen in most neoplasms and hyperproliferative lesions, but not normal skin. Survivin expression was often restricted to the upper third of the epidermis in psoriasis and lichen simplex chronicus, whereas all the other lesions stained diffusely. Survivin expression appears to be a consistent feature of keratinocytic neoplasms and hyperproliferative lesions and may contribute to the formation of epidermal hyperplasia seen in all of these disease states.

Proliferative characterization of basal-cell carcinoma and trichoepithelioma in small biopsy specimens

We examined the proliferative characteristics of 20 basal-cell carcinomas (BCCs) and 16 trichoepitheliomas (TEps) in an effort to understand and explore possible differences in their tumorigenic cell-cycle properties. These tumors were first compared for their expression of the nuclear proliferative protein Ki-67 and the tumor suppressor protein p53. We also compared the p53 downstream effector, p21(waf-1/cip-1), an inhibitor of cyclin-dependent kinases. The other p53-dependent, cyclin-dependent kinase inhibitor, p27(kip-1), has shown to be increased in TEps, which is consistent with this benign neoplasm's better-differentiated state. In our findings, we confirmed through immunohistochemical staining for Ki-67 that BCCs qualitatively showed a greater proliferative fraction compared to TEps (50.0 vs. 13.0%, p < 0.00001) as well as over-expression of p53 (2+ vs. 1+, p < 0.0008). BCCs marked by p21 demonstrated scattered nuclear positivity compared to the virtual absence of staining in the TEps (p < 0.019). In studying their cell-cycle properties, our findings suggest that abnormalities in the p53 pathway allow BCCs to obtain a growth advantage. We show that Ki-67 and p53 staining both appear useful in resolving challenging differential diagnoses and thereby help in directing appropriate treatment strategies.

Melanotrichoblastoma: immunohistochemical study of a variant of pigmented trichoblastoma

Trichoblastomas (TBs) are benign skin tumors recapitulating the differentiation of hair follicles. Several pathologic variants have been described, including the rare pigmented TB. We report a deeply pigmented nodular tumor excised on the scalp of a 32-year-old African woman, which was clinically suggestive of blue nevus or melanoma. Histologically, the tumor presented features of TB, remarkable by virtue of heavy melanin deposits found within and around tumor nests. By immunohistochemistry, abundant dendritic melanocytes with features of hair follicle melanocytes (expression of S100 protein, tyrosinase, and, most importantly, gp100/HMB-45) were found within the tumor masses. By analogy with melanoacanthoma, a tumor consisting of a combined proliferation of epidermal keratinocytes and melanocytes, we called this tumor "melanotrichoblastoma" and view it as a peculiar variant of (pigmented) TB.

Molecular and cellular biology of basal cell carcinoma

The finding of mutations in the PTCH gene in both Gorlin's syndrome and sporadic basal cell carcinomas has significantly advanced our understanding of the molecular defects that lead to the formation of these tumours. Knowledge of the specific molecular and functional changes that have taken place in these tumours will help us devise more defined therapies, as well as give us a better understanding of normal molecular pathways involved in skin development and function. The following is a summary of our current understanding of the molecular and cellular biology of basal cell carcinoma.

Isolation (from a basal cell carcinoma) of a functionally distinct fibroblast-like cell type that overexpresses Ptch

In this study we report on the isolation and characterization of a nonepithelial, nontumorigenic cell type (BCC1) derived from a basal cell carcinoma from a patient. The BCC1 cells share many characteristics with dermal fibroblasts, such as the expression of vimentin, lack of expression of cytokeratins, and insensitivity to agents that cause growth inhibition and differentiation of epithelial cells; however, significant differences between BCC1 cells and fibroblasts also exist. For example, BCC1 cells are stimulated to undergo DNA synthesis in response to interferon-gamma, whereas dermal fibroblasts are not. More over, BCC1 cells overexpress the basal cell carcinoma-specific genes ptch and ptch2. These data indicate that basal cell carcinomas are associated with a functionally distinct population of fibroblast-like cells that overexpress known tumor-specific markers (ptch and ptch2).

Bax expression and growth behavior of basal cell carcinomas

BACKGROUND

To understand the typical growth behavior of basal cell carcinoma (BCC) we searched for the correlation between proliferation and apoptosis and progression of BCC.

METHODS

Expression of Bcl-2, Bax, and Ki-67 was immunohistochemically investigated in both normal skin and BCC cells, as well as in the epidermis overlying BCC.

RESULTS

The results showed that in normal epidermis, Bcl-2 was homogeneously expressed in the basal cell compartment, whereas Ki-67 expression was largely restricted to the parabasal layer, the layer just above the basal cell layer, and exhibited a more scattered staining pattern. Bax was occasionally expressed in the basal layer and widely in the suprabasal compartment. Strikingly, the apparently normal epidermis overlying BCC showed an increased Bd-2 staining. In BCC, cells stained homogeneously for Bcl-2, whereas Bax and Ki-67 showed scattered staining patterns. Simultaneous expression was seen for Bcl-2 and Bax in 80 +/- 7% of the tumor cells, and co-expression of Bcl-2 and Ki-67 in 20 +/- 7% of the tumor cells. The cells expressing Bcl-2 and Ki-67, but lacking expression of Bax, the progressive fraction, comprised on average 7 +/- 3% of the tumor cell population.

CONCLUSION

These results suggest that this small progressive fraction of tumor cells, in combination with the relatively high percentage of cells still prone to apoptosis, can explain the indolent growth behavior of BCC.

Basaloid/follicular hyperplasia overlying connective tissue/mesenchymal hamartomas simulating basal cell carcinomas

BACKGROUND

Basaloid hyperplasia has been described overlying dermatofibromas as well as in the epidermis overlying nevus sebaceus. Although the morphology of these areas may resemble that of basal cell carcinoma (BCC), in the majority of cases aggressive behavior of the proliferation is not seen. In fact, the basaloid proliferation often shows follicular differentiation and may be stimulated and maintained by its relationship with the underlying stromal cells.

OBJECTIVE

We wanted to determine whether immunohistochemical staining for antibodies, which may suggest differences in pathogenesis, were different in basaloid hyperplasia overlying connective tissue/mesenchymal hamartomas and BCC.

METHODS

We report 3 cases of connective tissue/mesenchymal hamartomas with overlying basaloid hyperplasia, in which the areas of the basaloid proliferation showed follicular differentiation. Immunohistochemical stains included Ber-EP4, PCNA, Ki-67, Bcl-2, p53, SM-Actin, CD31, factor XIIIa, KP-1, and CD34.

RESULTS

There was a diffuse positive reaction for Ber-EP4 in all specimens and there was increased nuclear staining for PCNA and Ki-67. There was focal cytoplasmic staining for Bcl-2 in the areas of basaloid hyperplasia. Immunohistochemical staining for p53 showed only scattered positive cells except in a small focus in the areas of basaloid hyperplasia. The connective tissue component of all lesions showed diffuse staining for CD34 surrounding areas of basaloid hyperplasia in the mesenchymal component as well as in abundant S-100(+) nerves.

CONCLUSION

The areas of basaloid hyperplasia in these hamartomas exhibited an immature phenotype similar to that seen in both BCCs and follicular tumors; however, the patterns of proliferation markers, p53, Bcl-2, and the surrounding stromal cell markers were similar to those of benign follicular tumors. Thus the staining pattern for this group of antibodies suggests that areas of basaloid hyperplasia are not BCC.

Trichoepithelioma with "monster" stromal cells

Trichoepithelioma is a benign tumor of trichogenic origin which appears predominantly in childhood or in young adults. Different forms have been described according to clinical and histological features. The authors report a unique variant of trichoepithelioma arising on the limb of a 27-year-old man. The tumor was characterized by the mixture of an atypical fibroxanthomatous proliferation and basaloid epithelial strands of trichoepithelioma. Such histological features have not been previously reported. It raises the question of an additional variant of hair follicle tumor with a mixed epithelial and mesenchymal proliferation.

Trichoepithelioma papulosum multiplex

Trichoepithelioma papulosum multiplex is an uncommon autosomal dominant disorder in which multiple trichoepitheliomas are seen. Its cause may be a defective tumor suppressor gene. Studies have mapped this gene to the 9p21 locus. However, there is a parallel or identical syndrome of multiple trichoepitheliomas and cylindromas. Within a given family, some members may have cyclindromas whereas others may have trichoepitheliomas or a combination of both. Although preliminary evidence suggests a different gene is responsible, it is possible that TPM may be caused by more than two independent genes, with some cases of TPM due to impairment of the gene for cylindromatosis. This entity, as well as other disorders with multiple appendageal tumors, may require clarification and distinction from TPM.

An unusually aggressive trichoblastoma

Trichogenic tumors are neoplasms of the hair germ cell that usually exhibit benign behavior. We describe a case of a large invasive trichoblastoma requiring Mohs micrographic surgery for its removal. Immunohistochemical studies performed demonstrate overlapping features of this trichogenic tumor with basal cell carcinoma.

Ultraviolet and ionizing radiation enhance the growth of BCCs and trichoblastomas in patched heterozygous knockout mice

Basal cell carcinomas, the commonest human skin cancers, consistently have abnormalities of the hedgehog signaling pathway and often have PTCH gene mutations. We report here that Ptch+/- mice develop primordial follicular neoplasms resembling human trichoblastomas, and that exposure to ultraviolet radiation or ionizing radiation results in an increase in the number and size of these tumors and a shift in their histologic features so that they more closely resemble human basal cell carcinoma. The mouse basal cell carcinomas and trichoblastoma-like tumors resemble human basal cell carcinomas in their loss of normal hemidesmosomal components, presence of p53 mutations, frequent loss of the normal remaining Ptch allele, and activation of hedgehog target gene transcription. The Ptch mutant mice provide the first mouse model, to our knowledge, of ultraviolet and ionizing radiation-induced basal cell carcinoma-like tumors, and also demonstrate that Ptch inactivation and hedgehog target gene activation are essential for basal cell carcinoma tumorigenesis.

Trichoepithelioma: a 19-year clinicopathologic re-evaluation

Accurate histopathologic distinction between trichoepithelioma (TE) and basal cell carcinoma (BCC) may be challenging. From 97 cases diagnosed as TE during the period 1979-1997, 73 available cases were studied with regard to: 1) stroma; 2) retraction effect; 3) papillary-mesenchymal bodies (PMB); 4) amyloid; 5) mitotic figures; 6) apoptotic cells; 7) inflammation; 8) granuloma; and 9) calcification. A judgment was made regarding diagnosis. The patients' medical records were subsequently reviewed for clinical features and possible recurrence. The diagnosis of TE was confirmed histologically in 48 (65%) of 73 cases. Fifteen cases (21%) were reclassified as BCC (RC-BCC), eight other cases (11%) were reclassified as other lesions, and two additional cases (3%) could not be confidently classified as either TE or BCC. The most helpful differentiating features were the presence of retraction effect (in 100% of RC-BCC vs. 37% of TE), myxoid stroma (in 80% of RC-BCC vs. 12% of TE) and PMB (in 20% of RC-BCC vs. 81% of TE). Unexpected findings in TE were detection of amyloid in 33%, apoptotic cells in 100%, and mitotic figures in 46%. Five of the 15 RC-BCC have recurred (33%), whereas there have been no recurrences in the confirmed TE group. A constellation of histopathologic criteria may help to discriminate problematic examples of trichoepithelioma from basal cell carcinoma.

An immunohistochemical study of basal cell carcinoma and trichoepithelioma

The histologic distinction between tricheopithelioma and basal cell carcinoma may be difficult in small biopsies. Immunohistochemical stains have been used to help make this distinction; however, published studies have generally been limited to a few antibodies. To this end we performed a comprehensive immunohistochemical analysis of 20 basal cell carcinomas and 10 tricheopitheliomas from our files, in search of a consistent pattern of reactivity to distinguish the neoplasms in biopsies. The antibodies used were: low molecular weight keratin (Cam 5.2), Cytokeratin 7, (CK7), Cytokeratin 20, (CK20), Carcino-embryonic antigen (CEA), CD30 (Ki-1), bcl-2, Ham 56, HPCA-I (CD34), and Ulex Europaeus type I. In our study, bcl-2 stained all but one basal cell carcinoma in a diffuse pattern, whereas all tricheopitheliomas showed staining of the outermost epithelial layer. No other stain proved to be an independent marker for either neoplasm and no consistent immunohistochemical profile for either neoplasm emerged. Thus, we conclude that bcl-2 may be of some value in distinguishing basal cell carcinoma from tricheopithelioma, limited by the quantitative nature of the difference in staining. Histologic criteria applied to H&E-stained sections remain the cornerstone of histologic diagnosis.