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.     

Basal cell carcinoma and pilomatrixoma mirror human follicular embryogenesis as reflected by their differential expression patterns of SOX9 and β‐catenin

Background The current classification schemes of adnexal tumours are predominantly based on morphological and immunophenotypical similarities to adult skin structures, whereas a link between the embryology of the skin and the histogenesis of adnexal tumours has been largely neglected. Objective To describe the expression patterns of two proteins with proven relevance for hair follicle homeostasis (SOX9 and β‐catenin) during human cutaneous embryogenesis and to compare the findings with their expression in basal cell carcinoma (BCC) and pilomatrixoma. Methods Immunohistochemical evaluation with monoclonal antibodies against SOX9 and β‐catenin was carried out in embryonic and adult human scalp skin, and BCC and pilomatrixoma samples. Results We found that the expression patterns of SOX9 and β‐catenin during human hair follicle embryogenesis mirror the patterns in BCC and pilomatrixoma in spatial distribution within the various follicular subcompartments. Beginning with the hair peg stage, nucleocytoplasmic immunoreactivity of β‐catenin is exclusively confined to the emerging matrix (comparable to pilomatrixoma), whereas SOX9 is restricted to the primordial outer root sheath (comparable to BCC). Conclusions An appropriate immunophenotyping validated within the conceptual framework of cutaneous developmental biology allows a logical classification of adnexal neoplasms. Expanding this approach further has the potential to revise the current classification schemes so that not only BCC and pilomatrixoma but all adnexal tumours can be categorized logically.     

Desmoplastic trichoepithelioma: presentation of two cases

Trichoepithelioma is a benign neoformation with hair follicle differentiation that may clinically present in solitary, multiple or desmoplastic form. From a histopathological standpoint, it poses some diagnostic difficulties with basal cell carcinoma. We present two cases of desmoplastic trichoepithelioma, a rare adnexal tumor whose incidence is estimated at 2 per 10,000. Desmoplastic trichoepithelioma is a benign lesion, clinically and histologically similar to other dermatoses, and presents a true diagnostic challenge.     

Does the peritumoral stroma of basal cell carcinoma recapitulate the follicular connective tissue sheath?

Background: There are compelling embryologic and anatomic relationships within adnexal tumors. However, these are mostly perceived within the epithelial component while the stromal component of the tumors is frequently overlooked. In postnatal skin, nestin is almost exclusively expressed in the perifollicular mesenchyme. This study examines the expression of this neuroepithelial stem cell protein in trichoblastoma/trichoepithelioma and in basal cell carcinoma (BCC), which is increasingly being viewed as follicular in nature. Methods: We employed standard immunohistochemical methods with three different antibodies to examine the expression of nestin in 25 BCCs and compared the staining pattern with that of 7 trichoblastomas and 11 trichoepitheliomas. Results: Nestin is expressed in the peritumoral stroma of all tumors examined and is limited to the immediate layer of mesenchymal cells surrounding the tumor epithelium. In BCC, nestin‐immunoreactive cells are found as a sheath of thin, spindled fibroblasts, while reactive cells are plump in trichoepitheliomas/trichoblastomas. Conclusions: We postulate that the peritumoral stroma of BCC imitates the perifollicular connective tissue sheath, while in contrast that of trichoepithelioma/trichoblastoma is similar to the papillary and immediate peripapillary follicular mesenchyme. Further functional and animal experimental studies are needed to test this hypothesis. Sellheyer K, Krahl D. Does the peritumoral stroma of basal cell carcinoma recapitulate the follicular connective tissue sheath? A comparative analysis of nestin expression in basal cell carcinoma, trichoepithelioma, trichoblastoma and the hair follicle.     

Desmoplastic trichoepithelioma nosology. Reappraisal about a case developed on a varicella scar

We report the case of a 51-year-old woman who presented with a progressive elevation of the border of an old varicella scar. The lesion which was clinically diagnosed as a basal cell carcinoma turned out to be a typical desmoplastic trichoepithelioma. The development of desmoplastic trichoepithelioma in an area of scarring has not been previously reported. The nosology of this tumor is discussed with particular emphasis on its possible relationship to morphoeic basal cell carcinoma, thus questioning it as a true tumor sui generis.     

Immunohistochemical analysis of cytokeratin expression in various trichogenic tumors.

The immunophenotypes, especially expression of cytokeratins, in 13 cases of trichogenic tumors were examined to investigate their histogenesis. Four cases of multiple trichoepithelioma, five cases of classical solitary trichoepithelioma, one case of desmoplastic trichoepithelioma, one case of trichogenic trichoblastoma, one case of trichoblastic fibroma, and one case of giant solitary trichoepithelioma were retrieved. The immunoreactivities of the epithelial nests and the keratinous cysts in these tumors were similar to those of the outer root sheath and the infundibulum of normal hair follicles, respectively. From the comparative studies of the immunophenotypes with those of normal hair follicles, we speculated that all trichogenic tumors differentiate mainly toward the outermost layer of the outer root sheath between the lower part of the permanent portion and the upper part of the transient portion and some parts of them differentiate toward various other parts of the follicles. Although differentiation toward the other follicular structures can vary from case to case, there is no particular staining pattern specific for each kind of trichogenic tumor and no significant differences in immunoreactivity among them. Our observations support a recent notion that all neoplasms of follicular germinative cells should be grouped as a single entity.     

Congenital non-familial unilateral basaloid follicular hamartoma

Basaloid follicular hamartoma is not a well-recognized clinical entity and has often been diagnosed as trichoepithelioma or basal cell carcinoma. It is a unique benign follicular tumour which comprises a variety of clinical manifestations. We present the case of a 24-year-old male with unilateral basaloid follicular hamartoma present at birth and later misdiagnosed as basal cell carcinoma. Histological features of basaloid follicular hamartoma are not always diagnostic and clinico-pathological correlation is particularly important to distinguish this benign hamartoma from other basaloid tumours including basal cell carcinoma. Continuous follow-up of our patient did not reveal any clinical or histological malignant transformation.     

Sox9, more than a marker of the outer root sheath: spatiotemporal expression pattern during human cutaneous embryogenesis

Background: The sex‐determining gene Sox9 was recently unexpectedly found to have an essential role in outer root sheath differentiation. It was also characterized as a general marker of basal cell carcinoma. Herein, we describe its spatiotemporal expression pattern outside the hair follicle during human cutaneous embryogenesis. Methods: We examined immunohistochemically samples from embryonic and fetal human skin for the expression of SOX9 using standard techniques. For comparison reasons, we also included scalp skin from adults. Results: SOX9 is expressed in the developing nail organ, eccrine glands, blood vessels and melanocytes/melanoblasts. In the nail organ, the nail bed but not the nail matrix was immunoreactive for SOX9. In plantar skin, SOX9 specifically labels the evolving eccrine glands but not the interfollicular keratinocytes. Conclusions: The distinctive expression pattern of SOX9 during human cutaneous embryogenesis indicates a key role in skin homeostasis that includes but goes beyond its role in outer root sheath differentiation. Studying immunohistochemical markers in developing human skin has the potential to further our understanding of adult skin physiology and to deepen our concepts especially of the histogenesis of adnexal tumors (including those of the nail unit) and the relationship of the various adnexal structures to each other. Krahl D and Sellheyer K. Sox9, more than a marker of the outer root sheath: spatiotemporal expression pattern during human cutaneous embryogenesis.     

Basaloid follicular hamartoma: three cases with localized and systematized unilateral lesions

Two patients having a localized plaque of alopecia on the scalp, and one with a systematized unilateral epithelial nevus exhibited a histologically distinctive form of follicular hamartoma. In the affected areas individual hair follicles were replaced, or were associated with solid strands and branching cords of undifferentiated basaloid cells, filled in between by fibrous stroma resembling either a miniature premalignant fibroepithelial tumor of Pinkus, a small trichoepithelioma, or a basal cell epithelioma. The relation between these 3 patients and cases reported as linear unilateral basal cell nevus with comedones and generalized hair follicle hamartoma associated with myasthenia gravis is discussed.     

Immunohistochemical study of calretinin in normal skin and cutaneous adnexal proliferations

Calretinin is a calcium-binding protein member of the EF-hand family. The presence of calretinin has been demonstrated in certain stages of the cellular cycle in a wide variety of normal and neoplastic tissues. The main aims of our study were (1) to investigate what structures of the normal skin and cutaneous adnexal proliferations express immunoreactivity for calretinin and (2) to determine the value of immunohistochemical expression for calretinin as a marker for follicular, sebaceous, apocrine, and eccrine differentiation in cutaneous adnexal proliferations. We studied 139 biopsy specimens, including 10 cases of normal skin of different locations and 129 benign and malignant cutaneous adnexal proliferations. In normal skin, we found that calretinin is expressed in the innermost cell layer of the outer root sheath in anagen hair follicle, in both the duct and sebolemma of the sebaceous gland, in the secretory portion of eccrine glands, and in mast cells of the stroma. In cutaneous adnexal proliferations, we found strong immunoreactivity for calretinin in tricholemmal cysts, tricholemmomas/inverted follicular keratoses, tumors of follicular infundibulum, and in some basal cell carcinomas. Focal positivity was also seen in trichoadenomas, trichoblastomas/trichoepitheliomas, pilomatricomas, proliferating tricholemmal tumors, pilar sheath acanthomas, trichofolliculomas, follicular hybrid cysts, cutaneous mixed tumors, steatocystomas, sebaceous hyperplasias, and sebaceomas. These results demonstrate that immunohistochemical study for calretinin may be helpful to identify the innermost cell layer of the outer root sheath in anagen hair follicle and the cutaneous adnexal proliferations showing differentiation toward this structure. Calretinin immunoreactivity supports eccrine differentiation in some sweat gland neoplasms, and it is also useful in identifying neoplasms with ductal sebaceous differentiation.     

Desmoplastic trichoepithelioma and intradermal nevus: a combined malformation

We studied 13 desmoplastic trichoepitheliomas associated with intradermal nevi. Ten intradermal nevi were found among 76 new cases of desmoplastic trichoepithelioma (13%); three additional examples of the combined malformation were seen in consultation. Clinically, desmoplastic trichoepithelioma associated with an intradermal nevus was typically a small, firm or hard, sometimes annular, nodule on the face, particularly the cheek, of a relatively young woman. Microscopically, the combined malformation contained narrow strands of basaloid cells and keratinous cysts in a desmoplastic stroma, intimately mixed with intradermal nests of nevocytes. Melanocytic nevi have been associated with epidermal hyperplasia resembling seborrheic keratoses, follicular cysts, trichostasis spinulosa, syringomas, basal cell carcinomas, and hair follicle formation on the soles. The frequency of the occurrence of intradermal nevus with desmoplastic trichoepithelioma and the close anatomic association of the two elements may indicate that this combined malformation is another example of epithelial induction by melanocytic nevi.     

Keratin expression in basal cell carcinomas

The keratin phenotype of 15 cases of basal cell carcinoma was assayed immunohistochemically using a panel of monospecific antibodies to single keratin polypeptides. Whilst tumour tissue strongly expressed primary keratins 5 and 14 (normally synthesized in basal keratinocytes) no expression of secondary keratins 1 and 10 (characteristic of skin-type differentiation) was detected. Keratin 17, characteristic of the outer hair root sheath, was strongly expressed in all tumours. Keratin 19 was also normally expressed in parts of the hair follicle and was detected in four cases. The 'high cell turnover' keratin 16 was frequently induced in the overlying epidermis, but was rare within tumour tissue. No expression of simple epithelial keratins 8 and 18 was detected. Whilst the keratin phenotype of tumour cells is similar to that of basal cells within part of the hair root sheath, in keeping with suggestions of a follicular origin for basal cell carcinomas, the findings are also compatible with an origin from interfollicular pluripotent stem cells differentiating towards follicular structures.     

Immunohistochemical study of calretinin in normal hair follicles and tumors with follicular differentiation

BackgroundSelective immunostaining for calretinin labels the innermost layer of the outer root sheath of normal hair follicles, which is difficult to distinguish with hematoxylin-eosin staining.ObjectiveThe aim of this study was to determine whether immunohistochemistry for calretinin allows identification of cutaneous adnexal tumors with follicular differentiation towards cells of the outer root sheath.Material and methodsWe analyzed the staining pattern for calretinin by immunohistochemistry in 49 biopsies of cutaneous adnexal tumors with follicular differentiation.ResultsFifteen biopsies corresponded to trichilemmomas/inverted follicular keratosis and had staining for calretinin in the epithelium of the most superficial areas of the lesions and in squamous eddies. Ten were trichilemmal cysts, which displayed staining of the cyst wall. Three were basal cell carcinomas with variable staining according to the type of follicular differentiation in each variant. One was a panfolliculoma that had focal staining. Two were folliculosebaceous cystic hamartomas with staining of the excretory duct of the sebaceous glands. Two pilomatricomas and 3 proliferative trichilemmal tumors had positive staining in the cellular layers close to the lumen of the cystic structures. Nine trichoblastomas/trichoepitheliomas, 2 infundibular cysts, 1 dilated pore of Winer, and 2 acanthomas of the follicular sheath were negative for calretinin.ConclusionImmunohistochemistry for calretinin allows identification of cutaneous adnexal tumors of the hair follicle or a component of the follicle with differentiation towards cells of the outer root sheath.     

Monoclonal antibody Ber-EP4 reliably discriminates between microcystic adnexal carcinoma and basal cell carcinoma

BACKGROUND: Sclerosing cutaneous neoplasms often represent a diagnostic challenge. The monoclonal antibody Ber-EP4 recognizes two glycopolypeptides found in most human epithelial cells. It is diagnostically highly reliable in the differentiation between basal cell carcinoma and cutaneous squamous cell carcinoma. In this study, we report its application in the differential diagnosis of microcystic adnexal carcinoma, desmoplastic trichoepithelioma and basal cell carcinoma. METHODS: Biopsy samples from 28 sclerosing and infiltrating basal cell carcinomas, 13 microcystic adnexal carcinomas and 16 desmoplastic trichoepitheliomas were examined after immunohistochemical staining with Ber-EP4. RESULTS: Ber-EP4 did not label any of the microcystic adnexal carcinomas, whereas all 28 basal cell carcinomas were Ber-EP4 positive. Twenty-seven of the 28 showed moderate or strong staining intensity, with the majority being strong. Only one basal cell carcinoma was weakly positive. Twelve of the 16 desmoplastic trichoepitheliomas were immunoreactive with Ber-EP4 and the staining was more variable than those of basal cell carcinomas. CONCLUSIONS: Ber-EP4 reliably differentiates microcystic adnexal carcinoma from basal cell carcinoma to the same extent as it distinguishes the latter tumor from squamous cell carcinoma. While it stains the majority of desmoplastic trichoepitheliomas, these tumors still have to be considered in the differential diagnosis with microcystic adnexal carcinoma, when Ber-EP4 is applied.     

Basal cell carcinoma and stem cell markers : Contribution to possible histogenesis?

The prevalence and incidence of basal cell carcinoma are on the rise. Yet, its histogenesis is still controversial. Hitherto discussed concepts are largely based on morphological analogies. Historically, basal cell carcinoma was named after its similarity to the epidermal basal cell layer which is viewed as its histogenetic origin. On the other hand, a primitive follicular origin is postulated due to the morphological similarity of basal cell carcinoma to the embryonic hair germ. In 1990, the hair follicle bulge was characterized as the anatomical niche for follicular stem cells. Early studies employing stem cell markers suggested a follicular origin of basal cell carcinoma. Since then an explosion of stem cell markers has occured in dermatology. In this review, the stem cell markers employed in the examination of basal cell carcinoma up to now are critically evaluated. Initially, studies on the histogenesis of this common dermatological tumor are reviewed.     

CD-34 and Ki-67 staining patterns of basaloid follicular hamartoma are different from those in fibroepithelioma of Pinkus and other variants of basal cell carcinoma

BACKGROUND AND AIMS: Basaloid follicular hamartoma is a rare disorder regarded as a developmental malformation. It may be solitary or generalized, linear or regionalized, and is sometimes associated with myasthenia gravis or alopecia. We compared immunohistochemical staining patterns of selected markers in order to differentiate this hamartoma from fibroepithelioma of Pinkus, a basal cell carcinoma variant it can be confused with. METHODS: The expression of three immunohistochemical markers--CD-34, Ki-67, bcl-2--was studied in a basaloid follicular hamartoma and in a fibroepithelioma of Pinkus. Two basal cell carcinomas, a nodular and a fibrosing type, and a trichoepithelioma were included as controls. RESULTS: Basaloid follicular hamartoma shows a low proliferation index and an at least focally circumferential expression of CD-34 around the epithelial strands. This compares to the findings in trichoepithelioma. In contrast, fibroepithelial tumor of Pinkus and two other basal cell carcinoma subtypes display a high proliferative index and an absence of CD-34 expression around the epithelium. These findings support the non-neoplastic nature of basaloid follicular hamartoma.     

Bcl-2, CD34 and CD10 expression in basaloid follicular hamartoma, vellus hair hamartoma and neurofollicular hamartoma demonstrate full follicular differentiation

Generalized basaloid follicular hamartoma syndrome (GBFHS) is a rare, recently-described, autosomal-dominantly inherited disorder that presents with disseminated milia, palmoplantar pitting, hypotrichosis and basaloid follicular hamartomas (BFH). BFH is a benign adnexal tumor that resembles basal cell carcinoma (BCC). In this study, we report two cases of GBFHS and stain BFH, a vellus hair hamartoma (VHH) and a neurofollicular hamartoma (NH) with CD34, bcl-2 and CD10 to characterize and compare the staining patterns of these follicular tumors. Standard immunohistochemistry labeling with CD34, bcl-2 and CD10 was performed on paraffin-embedded, formalin-fixed tissue sections of five BFH (four for CD10), one VHH and one NH. CD34 stromal staining was observed in all specimens. Bcl-2 stained the outermost cell layers of the basaloid nests in all specimens. CD10 stained the peritumoral stroma of all specimens. The BFH, NFH and the VHH showed CD10 staining of matrical cells. CD34 and CD10 stain peritumoral stroma of BFH, VHH and NH. Bcl-2 stains the outermost cell layer of these tumors. CD10 was also observed to stain matrical cells. These results show the similarities in differentiation between these benign follicular neoplasms and trichoepithelioma.     

Immunohistochemical study of angiotensin receptors in human anagen hair follicles and basal cell carcinoma

BACKGROUND: Angiotensin receptors are the specific receptors of angiotensin II of the renin-angiotensin system. However, expression of the receptors in hair follicles has not been determined. OBJECTS: To clarify the expression and localization of angiotensin receptors in human anagen hair follicles and basal cell carcinomas. METHODS: We studied immunohistochemically the expression of angiotensin type 1(AT1) and type 2 (AT2) receptors in human anagen hair follicles and in 16 cases of basal cell carcinoma (BCC) (nine of solid BCC of the circumscribed type, two of adenoid BCC, five of BCC with follicular differentiation). RESULTS: Our experiments demonstrated the localization of AT1 in the inner root sheath and the inner layers of the outer root sheath. In BCC, positive staining with AT1 was revealed in the tumour cells of basal cell carcinoma with follicular differentiation. CONCLUSIONS: AT1 may have a role in association with follicular keratinization. Studying AT1 distribution may be useful in understanding the pathophysiology of human hair follicles and the hair follicle-associated tumours.     

Cytokeratin 15 expression in trichoepitheliomas and a subset of basal cell carcinomas suggests they originate from hair follicle stem cells

Trichoepitheliomas and many basal cell carcinomas appear to arise from the hair follicle, and in particular from the hair follicle bulge. This histogenesis is suggested from both morphological and immunohistochemical studies on tumor cells and stroma. Epithelial stem cells are thought to be important in tumorigenesis, and we previously localized a population of stem cells to the bulge area of the outer root sheath. We recently identified an anti-CD8 monoclonal antibody (DAKO clone C8/144B) that cross-reacts with cytokeratin 15 (K15), and serves as a specific marker for the bulge. In this study, we screened a series of trichoepitheliomas (n=13), basal cell carcinomas (n=37) and a variety of other skin tumors with this antibody. All trichoepitheliomas (100%) showed keratin 15 expression, while only a subset of basal cell carcinomas (27%) was K15-positive. Epidermal tumors, including squamous cell carcinomas, were K15-negative. Tumors of follicular derivation such as proliferating trichilemmal cysts were also K15-positive, while others such as pilomatricoma were K15-negative. Expression of K15 in trichoepitheliomas, some basal cell carcinomas and other follicular tumors suggests that these tumors are related to hair follicle stem cells in the bulge.     

Multiple Basaloid Cell Hamartoma with Alopecia and Autoimmune Disease (Systemic Lupus Erythematosus)

We report a 22-year-old Japanese woman with multiple basaloid cell hamartoma with alopecia and autoimmune disease (systemic lupus erythematosus). She presented with infiltrated large annular, brown-violet, erythematous plaques with atrophic areas in the center on her right cheek, left abdomen and left knee. She also had progressive multiple follicular keratotic papules on her scalp, face, neck, and both axilla and hair loss from her scalp, eyebrow, and axilla. Serologically, reumatoid factor (+++), rheumatoid arthritis hemagglutination test (x1280), and anti-nuclear antigen (x160) were positive. Histological findings of the annular lesion showed liquefaction degeneration of basal cells, lymphocytic infiltration around hair follicles and capillaries, and panniculitis with lymphoid cell infiltration, which was diagnosed as lupus erythematosus profundus. The histological findings of multiple follicular papular lesions of the scalp and neck showed aggregations of basaloid cells, partially with hair-bulb-like structures, which was diagnosed as trichoepithelioma. Taken together, the histogenesis of multiple basaloid cell hamartoma is thought to share the same basis with autoimmune disease.