Desmoplastic trichoepithelioma versus morphoeic basal cell carcinoma: a critical reappraisal of histomorphological and immunohistochemical criteria for differentiation

Clinical and Molecular Features of Morpheaform Basal Cell Carcinoma: A Systematic Review

Basal cell carcinoma (BCC) is the most common skin cancer, with a lifetime risk currently approaching up to 40% in Caucasians. Among these, some clinical and pathological BCC variants pose a higher risk due to their more aggressive biological behavior. Morpheaform BCC (morBCC), also known as sclerosing, fibrosing, or morpheic BCC, represents up to 5-10% of all BCC. Overall, morBCC carries a poorer prognosis due to late presentation, local tissue destruction, tumor recurrence, and higher frequency of metastasis. In this systematic review, we review the epidemiological, clinical, morphological, dermatoscopical, and molecular features of morBCC. After the title and abstract screening of 222 studies and the full-text review of 84 studies, a total of 54 studies met the inclusion criteria and were thus included in this review.

Desmoplastic Trichoepithelioma With Pseudocarcinomatous Hyperplasia: A Folliculosebaceous Neoplasm in Young Persons

ABSTRACT

Pseudocarcinomatous desmoplastic trichoepithelioma (PDTE) features verrucous squamous epidermal hyperplasia with a jagged undersurface overlying cords of follicular germinative cells in a fibrotic stroma. To date, only 5 cases have been reported. We identified 7 new PDTEs from 2 institutions and reviewed their clinical manifestations and immunohistochemical profile. The median age was 14 years (range 8-34 years). New findings included vacuolization of the basal layer of the pseudocarcinomatous surface epithelium, and the frequent presence of singly distributed sebocytes within the cords of basaloid cells. The immunohistochemical profile resembles desmoplastic trichoepithelioma, with expression of TDAG51, CK15, and Ber-Ep4. Colonizing CK20+ Merkel cells were present in all cases. PDTE needs to be differentiated from malignant neoplasms such as squamous cell carcinoma, morphoeic basal cell carcinoma, and microcystic adnexal carcinoma. Recognizing the features of this sclerosing folliculosebaceous neoplasm facilitates accurate diagnosis and avoids overtreatment.

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.

Differential diagnostic significance of epithelial and stromal CD10 expression in tumors of trichogenic origin

BACKGROUND AND OBJECTIVES

The histological differential diagnosis between benign trichogenic skin tumors and basal cell carcinoma may be challenging. We therefore set out to investigate whether expression of CD10, a cell surface protein with neutral endopeptidase activity, might be a suitable marker for the histological differential diagnosis of trichogenic skin tumors.

PATIENTS AND METHODS

We immunohistochemically analyzed 119 cases of benign trichogenic skin tumors and basal cell carcinoma. These included 28 nodular and 15 sclerosing basal cell carcinomas, 21 Pinkus tumors, 20 trichoblastomas, nine trichofolliculomas, eleven trichoepitheliomas, five desmoplastic trichoepitheliomas, and ten seborrheic keratoses.

RESULTS

The majority of nodular basal cell carcinomas expressed CD10 in tumor cells at the peripheral (22/28 [75 %]). On the other hand, trichoblastomas revealed peripheral CD10 expression in only 10 % (2/20) of cases, whereas 50 % showed central expression (10/20). Peripheral epithelial expression of CD10 was also found in Pinkus tumors (9/21 [42.9 %]) and trichoepithelioma (4/11 [36.4 %]). Desmoplastic trichoepithelioma showed no tumoral CD10 expression at all (0/5 [0 %]), while the majority of sclerosing basal cell carcinomas was positive for CD10 (13/15 [86.7 %]).

CONCLUSIONS

Our findings suggest that epithelial expression of CD10 - and not peritumoral stromal CD10 expression, as has been postulated - may well be of differential diagnostic significance. The pattern of distribution of CD10-positive neoplastic cells in particular can be useful in the diagnosis of trichogenic tumors.

Cutaneous Squamous Cell Carcinoma With Sclerosing Features: An Uncommon and Potentially Aggressive Variant

Sclerosing squamous cell carcinoma (SCC), also known as "desmoplastic" SCC, is a rare subtype of cutaneous malignancy. This variant is clinically significant because it is associated with an increased risk of local recurrence and metastasis. We herein present 16 examples of sclerotic SCC of the skin in 8 men and 3 women, with a median age of 66 years. The most common site of origin for this tumor is the skin of the head and neck, including the scalp (5 tumors in 2 different patients), forehead (3 cases), nasal ala (2 cases), neck (2 cases in the same patient), ear (2 cases), cheek (1 case), and chest (1 case). Microscopically, sclerosing SCCs are characterized by cellular cords, nests, and islands, as well as scattered single cells infiltrating densely desmoplastic and collagenized connective tissue. The differential diagnosis principally includes sclerosing basal cell carcinoma, microcystic adnexal carcinoma, and desmoplastic trichoepithelioma. The main goals of this study are to further characterize these lesions pathologically, and increase general awareness of this SCC subtype.

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.

p40 in Conjunction With CK20 and E-Cadherin Distinguishes Primary Adnexal Neoplasms of the Skin

Although basal cell carcinomas (BCC) show typical histomorphologic features, they sometimes remain difficult in distinction from benign adnexal skin tumors of follicular origin like trichoepithelioma (TE) or trichoblastoma (TB). Consequently, an immunohistochemical marker panel separating described entities would be helpful in clinical routine. Thus, we stained 22 skin lesions (BCC, TE, and TB) against β-catenin, CK20, E-cadherin, p40, and p63. The staining pattern was described and quantified using an immunohistochemical score. Although p40 and p63 revealed a strong staining intensity of all skin lesions without distinction between BCC and benign lesions (P=1.000), established Merkel cell marker CK20 illustrated a loss of staining in BCC compared with TE and TB (P=0.007). In contrast, BCC exhibited an increased expression of E-cadherin in relation to TE and TB (P=0.009). Single application of CK20 or E-cadherin could predict diagnosis of BCC in 81.8% or 72.7%, respectively. Combining consecutive staining of E-cadherin and CK20 could even enhance specificity toward diagnosis of TE or TB. Hence, findings of our study imply that sequential staining of CK20 and E-cadherin prevents false-positive classification of BCC. Furthermore, our study demonstrated that p40 exhibits the same staining pattern in BCC, TE, and TB. Therefore, p40 might replace p63 equivalently establishing diagnosis of primary adnexal neoplasms of the skin in the form of BCC as well as benign adnexal tumors. As a result, the depicted immunohistochemical marker panel may be applied for adnexal skin neoplasms as a diagnostic adjunct especially in surgically challenging body regions.

Fibroepithelioma of Pinkus Revisited

Background

Fibroepithelioma of Pinkus (FeP) is considered a variant of basal cell carcinoma (BCC); however, in the past 20 years, some researchers have argued for its classification as a trichoblastoma. Recently, use of a new immunostaining marker and further dermoscopic characterization of FeP have advanced the debate about its proper classification.

Purpose

A review of the evidence for and against classification of FeP as BCC or trichoblastoma is presented.

Methods

Using PubMed, the term FeP was searched and relevant citations were assessed. Additional relevant articles were identified from references of key papers.

Results

FeP shares characteristics of both trichoblastoma and BCC.

Conclusion

Derived from the same cell type, BCC and trichoblastoma may be best considered as representing opposite ends of a spectrum of differentiation, with FeP deserving an intermediate classification.

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.

Basal cell carcinomas showing histological features generally associated with cutaneous adnexal neoplasms

Basal cell carcinoma (BCC) is the commonest malignant neoplasm in humans. Although a histopathological diagnosis of BCC is straightforward in the vast majority of cases, unusual histological variants can present a diagnostic challenge. A small proportion of BCCs show features which are generally associated with cutaneous adnexal neoplasms. Such changes may involve either the epithelium or the stroma and can mislead the pathologist particularly in small biopsies. Despite the growing evidence which speculate that BCC is a primitive follicular tumor, it is unusual to encounter tumors which actually show definitive signs of adnexal differentiation. This review aims to address this somewhat overlooked aspect of a very common tumor and offers practical guidance to distinguish them from adnexal neoplasms which they might mimic.

Desmoplastic trichoepithelioma: A clinicopathological study of three cases and a review of the literature

Desmoplastic trichoepithelioma (DTE) is a rare benign adnexal tumor with the characteristic features of asymptomatic, solitary, annular, indurated and centrally depressed papules or plaques, most commonly occurring in younger individuals on the face. Microscopically and clinically, DTE may be difficult to distinguish from other cutaneous adnexal neoplasms, particularly syringoma, cutaneous metastatic breast cancer, morpheaform basal cell carcinoma and microcystic adnexal carcinoma. The present study reports three cases of DTE. The first case was of a 45-year-old male with an asymptomatic flesh-colored plaque below the right edge of the outer canthus that had been present for seven years. The second case was of a 23-year-old female with an asymptomatic skin lesion on the right cheek that had slowly and progressively increased in size. The third case was of a 26-year-old female who presented with a hard yellowish-white plaque, which gradually grew and formed a rectangular, 3×4-cm patch, on the tip of the left brow. This plaque was present for three years without evident cause or subjective symptoms. In all three cases, the routine systemic examinations and laboratory findings were normal. Histopathological and immunohistochemical findings from incisional biopsies of the lesions were consistent with a diagnosis of DTE. DTE treatment methods and immunohistochemical markers were analyzed by reviewing clinical pathological aspects in order to avoid a misdiagnosis and to provide the best available treatment approach for DTE.

Immunohistochemistry in dermatopathology

CONTEXT

Immunohistochemistry is not a diagnostic test but a highly valuable tool that requires interpretation within a context.

OBJECTIVE

To review the current status and limitations of immunohistochemistry in dermatopathology.

DATA SOURCES

English-language literature published between 1980 and 2014.

CONCLUSIONS

Although immunohistochemistry is rarely completely specific or sensitive, it is an important adjunctive technique in dermatopathology and can be helpful in a series of diagnostic dilemmas.

Diagnostic Immunohistochemistry in Cutaneous Neoplasia: An Update

Immunohistochemistry (IHC) is an important adjunct in the diagnosis of neoplastic skin diseases. In addition to the many established IHC markers currently in use, new markers continue to emerge, although their general acceptance and routine application requires robust validation. Here, we summarize the most well-established and commonly used biomarkers along with an array of newer ones reported in the past several decades that either demonstrate or hold high clinical promise in the field of cutaneous pathology. We also highlight recent applications of novel IHC markers in melanoma diagnosis including genetic mutation status markers [e.g. BRAF (v-raf murine sarcoma viral oncogene homolog B) and NRAS (neuroblastoma RAS viral oncogene homolog)] and an epigenetic alteration marker (e.g. 5-hydroxymethylcytosine). We specifically focus on the role of IHC in the differential diagnosis of cutaneous lesions that fall under the following categories: melanoma, epidermal tumors with an intraepidermal epitheliomatous pattern, spindle cell lesions of the dermis, small round blue cell tumors of the dermis, and cutaneous adnexal tumors. While IHC is a valuable tool in diagnostic dermatopathology, marker selection and interpretation must be highly informed by clinical context and the histologic differential diagnosis. With rapid progress in our understanding of the genetic and epigenetic mechanisms of tumorigenesis, new IHC markers will continue to emerge in the field of diagnostic dermatopathology.

Benign subclinical syringomatous proliferations adjacent to a microcystic adnexal carcinoma: a tumor mimic with significant patient implications

Microcystic adnexal carcinoma (MAC) is an uncommon, locally aggressive, malignant cutaneous tumor with pilar and eccrine differentiation. Mohs micrographic surgery is the treatment of choice for this condition, but specific histological findings can complicate MAC removal and leave doubt as to whether the tumor has been completely removed. Here we describe the clinical and pathological characteristics of a case in which a patient with an MAC underwent multiple reexcisions because of the presence of benign subclinical syringomatous proliferations adjacent to the primary lesion. Our case raises awareness of syringomatous proliferation, a benign process histologically similar but behaviorally distinct from a primary MAC. This experience highlights the importance of continued communication between dermatopathologists and dermatologic surgeons in providing quality patient care.

[Fundamentals of cutaneous adnexal tumors]

Adnexal tumors of the skin are epithelial skin tumors with differentiation towards the adnexal epithelial structures of the skin, namely, hair follicle, sebaceous gland, apocrine gland, and eccrine gland. Adnexal tumors include hamartomas, benign and malignant neoplasms, and hyperplasias. The specific diagnosis of adnexal tumors is important because some lesions such as sebaceous neoplasms, cylindromas, or fibrofolliculomas are herald lesions of hereditary tumor syndromes (e.g., Muir-Torre syndrome, familial cylindromatosis, Birt-Hogg-Dubé syndrome). In this article, the classification of adnexal tumors of the skin is explained on the basis of embryology and histology and the main features of tumor-associated syndromes are summarized. Moreover, some conceptual controversies and problems in differential diagnosis of cutaneous adnexal tumors are discussed.

What is new in adnexal tumors of the skin?

This article reviews the recent dermatopathology literature regarding cutaneous adnexal neoplasms, with emphasis on new and underrecognized entities, "old entities" with new findings, advances in immunohistochemistry, and new findings in relation to inherited disorders associated with cutaneous adnexal neoplasms.

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.

Diagnostic utility of cytokeratin 17 immunostaining in morpheaform basal cell carcinoma and for facilitating the detection of tumor cells at the surgical margins

BACKGROUND

The morpheaform subtype of basal cell carcinoma (BCC) often presents a diagnostic histological challenge, and its true margin may be difficult to determine with accuracy. This tumor may also be difficult to distinguish from other adnexal neoplasms having a benign clinical course. Previous work has shown that cytokeratin 17 (CK17 or K17) expression is high in BCC.

OBJECTIVE

To confirm the expression of K17 across the subtypes of superficial, nodular and morpheaform BCC variants and to compare K17 expression in each of these subtypes of BCC with that in two other adnexal neoplasms.

METHODS

Tissue specimens from each tumor category were randomly collected, immunolabeled, and scored for K17 expression according to intensity and extent of immunostaining.

RESULTS

Our results indicate that K17 is a useful marker in the identification and outlining of BCC. Moreover, in morpheaform BCC, K17 immunostaining clearly detected individual tumor cells well away from the dermal tumor strands that otherwise seemed nonmalignant according to hematoxylin and eosin staining alone. In addition, the expression of K17 in morpheaform BCC is capable (100% of specimens; p < .001) of distinguishing this tumor from desmoplastic trichoepithelioma.

CONCLUSION

We propose that K17 immunostaining could improve the diagnostic and surgical management of these tumors.

Role of immunohistochemistry in diagnosing tumors of cutaneous appendages

In recent years, there has been significant progress in immunohistochemistry as an ancillary tool in diagnostic dermatopathology. In most instances, the histologic diagnosis can be rendered with the routine histologic sections; however, immunohistochemistry can help to narrow the differential in diagnosing neoplasms of cutaneous appendages in some settings including adnexal versus epidermal origin, benign versus malignant adnexal neoplasms, and primary adnexal carcinoma versus cutaneous metastases as outlined in this review.

Desmoplastic trichoepithelioma: report of a unique periocular case

In a 58-year-old woman with blepharospasm, a slowly enlarging left inferomedial eyelid lesion developed. It measured 3 × 5 mm and was nonulcerated, well-circumscribed, whitish, upraised, and firm. An initial incomplete excision followed by a total repeated excision revealed small squamous microcysts, often exhibiting calcifications and cords of nonclefting basaloid cells embedded in a scirrhous stroma characteristic of desmoplastic trichoepithelioma (DTE). Immunohistochemical investigations disclosed CD34-positive stromal fibroblasts and many CK20-positive Merkel cells located among the epithelial cells, features absent in mimicking sclerosing basal cell carcinoma (BCC). The tumor has not recurred during 6 months of follow up. Besides BCC, the differential diagnosis chiefly concerns syringoma and microcystic adnexal carcinoma. Surgical therapy should aim at complete excision but does not have to be as extensive or aggressive as that used for morpheic or sclerosing BCC because of its lack of diffusely infiltrating margins.

Fibroepithelioma of Pinkus is a true basal cell carcinoma developing in association with a newly identified tumour-specific type of epidermal hyperplasia

BACKGROUND

Fibroepithelioma of Pinkus (FEP) has long been viewed as a subtype of basal cell carcinoma (BCC). Recently, however, the proposal has been made that FEP represents a fenestrated trichoblastoma/trichoepithelioma. One of the main arguments is the presence of Merkel cells in FEP, which typically do not occur in BCC.

OBJECTIVES

As the new stem cell marker, PHLDA1 (TDAG51), labels trichoepithelioma but not BCC, our aim was to characterize its staining pattern in FEP. Because adnexal tumours have been viewed as recapitulating embryogenesis, we also examined PHLDA1 immunoreactivity in the skin of human embryos and fetuses.

METHODS

We studied immunohistochemically PHLDA1 staining in 31 FEPs, 14 BCCs and 16 trichoepitheliomas and compared this with its staining pattern in embryonic skin and with the distribution of Merkel cells.

RESULTS

In FEP, PHLDA1 labels the anastomosing network of thin cellular strands but not the basaloid nubbins. During embryogenesis, PHLDA1 stains the basal cell layer of the epidermis, as long as adnexal structures develop. Immunoreactivity for PHLDA1 correlates positively with the presence of Merkel cells.

CONCLUSIONS

We propose that the thin anastomosing network of PHLDA1-positive cells represents a type of epidermal hyperplasia specific to FEP. The multifocal BCCs that are PHLDA1-negative develop from this network which becomes incorporated into the tumour. Viewing the anastomosing network as a tumour-specific form of epidermal hyperplasia explains the hitherto enigmatic presence of Merkel cells in FEP.

Basal cell carcinoma: cell of origin, cancer stem cell hypothesis and stem cell markers

Cancer stem cells have recently been described in several high-grade neoplasms. It is still unclear if they also occur in cutaneous malignancies. Cancer stem cells are not identical with somatic stem cells. The presence of tumour stem cells in a neoplasm does not in itself equal that the tumour derives from a somatic stem cell. A cell originally lacking stem cell characteristics could also acquire those features during the course of carcinogenesis and then becomes the clonal founder cell of a tumour. Basal cell carcinoma (BCC) is the most common cutaneous malignancy. A plethora of various stem cell markers has been applied to study its cellular origin. Intriguingly, the anatomical origin of BCC is still uncertain. This review will discuss the various stem cell markers used in BCC and the cellular origin of this tumour, and touches briefly on the possibility of cancer stem cells in BCC. If BCC or other skin cancers harbour tumour stem cells, these cells could be specifically targeted, making use of specific cell surface molecules such as receptor proteins. Novel drugs directed against those receptor proteins could replace currently available shotgun approaches including imiquimod.

Desmoplastic trichoepithelioma confused with cutaneous squamous cell carcinoma in childhood

Squamous cell carcinoma of the skin is very rare in childhood, especially without predisposing factors or underlying diseases. We report the case of a desmoplastic trichoepithelioma misdiagnosed as cutaneous squamous cell carcinoma in a 12 years old boy Only accurate multiple reviews of the histological samples and repeated questioning of the mother could finally clarify the diagnostic dilemma. Desmoplastic trichoepithelioma is a quite uncommon benign adnexal tumor with a reported incidence, in adults, of 1 in 5000 skin biopsies. It usually affects the face of middle-aged women, but it has been reported at any age. The treatment of desmoplastic thricoepithelioma includes curettage and electrodesiccation or surgical removal. Recurrence or appearance of new lesions is rare. The diagnosis of squamous cell carcinoma in a child without predisposing factors should be accepted with great caution and only after expert histological review.

PHLDA1 (TDAG51) is a follicular stem cell marker and differentiates between morphoeic basal cell carcinoma and desmoplastic trichoepithelioma

BACKGROUND

Morphoeic basal cell carcinoma (BCC) and desmoplastic trichoepithelioma can often be difficult to differentiate on routine sections and few reliable immunohistochemical markers are currently available. Recent cDNA microarray studies revealed the pleckstrin homology-like domain, family A, member 1 protein (PHLDA1) as a highly reliable marker of the hair follicle stem cells. Given the differentiation of trichoepithelioma along the follicular lineage and the proposed role of PHLDA1 as a follicular stem cell marker, we examined the staining pattern of PHLDA1 in the desmoplastic variant of trichoepithelioma and in its differential diagnostic conundrum, morphoeic BCC.

OBJECTIVES

To describe the expression pattern of PHLDA1 in morphoeic BCC and desmoplastic trichoepithelioma.

METHODS

Evaluation of the staining pattern for PHLDA1 was performed using standard immunohistochemical techniques. For comparison reasons, we analysed staining for PHLDA1 in normal skin structures with particular reference to the hair follicle.

RESULTS

With the exception of one case, all 16 desmoplastic trichoepitheliomas were immunoreactive with more than 80% of the cells stained, whereas all 14 morphoeic BCCs were PHLDA1-negative with the exception of ulcerated tumours. In the latter, the tumour islands close to the ulcer were PHLDA1-positive whereas the deeper located tumour portions remained immunonegative. PHLDA 1 was prominently expressed in the hair follicle bulge of terminal and vellus hair follicles.

CONCLUSIONS

The hair follicle bulge marker PHLDA1 differentiates between desmoplastic trichoepitheliomas and nonulcerated examples of morphoeic BCCs. We suggest incorporating PHLDA1 in the diagnostic work-up of difficult to differentiate basaloid tumours.

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.

Desmoplasia: not always a bad thing

Desmoplasia describes a histological pattern characterized by a hyalinized stroma and a minimal cellular infiltrate. In non-cutaneous neoplasms, this pattern of stromal response is classically associated with malignancy, whereas in cutaneous pathology, desmoplasia is observed in malignant as well as benign neoplasms. Given this, the obvious question is whether desmoplasia associated with a benign neoplasm is any different from that associated with malignant tumours. Is the stromal response a mere epiphenomenon, or does it actually contribute to the biological behaviour of the neoplasm? What happens at the tumour-host interface? Which molecules are involved in mediating the desmoplastic reaction pattern? This review is an attempt to answer these questions. Examples of benign and malignant cutaneous neoplasms associated with the desmoplastic reaction pattern will be included.

[Desmoplastic trichoepithelioma: a clinicopathological study, including a comparison with morpheiform basal cell carcinoma]

BACKGROUND

Desmoplastic trichoepithelioma (DTE) is an uncommon form of adnexal tumour that was described for the first time as a separate clinicopathological entity in 1976. We carried out a retrospective histopathological study of a large series of cases of DTE in order to better characterise this tumour and compare it with sclerodermiform basal cell carcinoma (BCC), which is in fact the most common as well as the most complex type of differential diagnosis.

PATIENTS AND METHODS

We included in this study all cases of DTE diagnosed between 1979 and 2001 at our dermatopathology laboratory. The clinical features were taken from the patient files. Diagnosis was confirmed by two different examiners and all microscopic elements were reviewed. The same clinical and demographic data were collected for cases of BCC diagnosed over the same period.

RESULTS

We included 68 cases of DTE in 67 patients in our study, of whom 83.5% were women, and the mean age was 42.8 years. Lesions were found primarily on the head (98.5% of cases), mainly on the cheeks (29.2% of cases) and forehead (23.1% of cases). The diagnosis was only made by the clinician in four cases; in 38 cases the diagnosis made was BCC. In all cases, histological examination revealed thin lines of basaloid epithelial cells associated with small keratinising cysts. A common finding was granulomas with foreign bodies and calcifications. In six cases (8.8%), a tumour combining DTE with an intradermal naevus was observed. Mean clinical follow-up of 8 years (1 to 23 years) in 29 patients showed absence of relapse or metastasis. Over the same period, 662 cases of BCC were recorded in 499 patients, 58.9% of whom were women. The mean age was 65.6 years. The principal location was the nose (34% of cases). No cases of associated naevus were recorded.

COMMENTS

DTE is a firm plaque-like lesion, flesh coloured or yellowish, and generally with a depressed centre; it is seen primarily in middle-aged women and occurs principally on the cheeks and forehead. There is a significant association with naevus, a singular feature among adnexal tumours. On average, it is 10 times less common than BCC. The size of our study groups shows for the first time distinguishing features with regard to BCC, for which the age of onset is far higher and predominance among women less marked. Further, the sites are different, with BCC being seen predominantly on the nose while DTE is seen mainly on the cheeks. A suggested clinical diagnosis is thus possible.