Basaloid tumors in nevus sebaceus revisited: the follicular stem cell marker PHLDA1 (TDAG51) indicates that most are basal cell carcinomas and not trichoblastomas.

BACKGROUND: Until the 1990s, basal cell carcinoma (BCC) was viewed as the most common epithelial neoplasm developing in association with nevus sebaceus (NS). Currently, trichoblastoma is thought of as the most prevalent basaloid neoplasm in NS. The follicular stem cell marker pleckstrin homology-like domain, family A, member 1 (PHLDA1) also known as T-cell death-associated gene 51 (TDAG51) labels trichoepithelioma (TE) but not BCC. Therefore, we explored its usefulness in basaloid neoplasms developing in NS. METHODS: We studied immunohistochemically PHLDA1 in 10 nodular BCCs, 11 TEs, 11 trichoblastomas and 25 NS with basaloid tumors. Additionally, we examined the expression of BCC marker BerEP4 and the distribution of Merkel cells that function as surrogate markers for benign follicular neoplasms. RESULTS: Nineteen of the 25 basaloid tumors in NS were PHLDA1-negative comparable to BCC arising de novo and six tumors were PHLDA1-positive comparable to solitary trichoblastomas and TEs. Fewer Merkel cells were seen in BCCs associated with NS when compared with trichoblastoma. BerEP4 did not discriminate between the neoplasms. CONCLUSIONS: We raise concern that the unquestioned assessment that basaloid tumors developing in association with NS represent mostly trichoblastomas and not BCC may not be true. This influences clinical care, as it is paramount in the decision of whether to excise these lesions or not.

The immunohistochemical differential diagnosis of microcystic adnexal carcinoma, desmoplastic trichoepithelioma and morpheaform basal cell carcinoma using BerEP4 and stem cell markers.

BACKGROUND: Microcystic adnexal carcinoma (MAC), desmoplastic trichoepithelioma (DTE) and morpheaform basal cell carcinoma (BCC) frequently impose a considerable differential diagnostic challenge and immunohistochemistry is often used as a differentiating diagnostic adjunct. METHODS: Using standard immunohistochemical techniques, we examined 21 examples of DTE, 17 examples of morpheaform BCC and 10 examples of MAC for the expression of BerEP4, a marker of epithelial cells, and of three stem cell markers, pleckstrin homology-like domain, family A, member 1 (PHLDA1) [T cell death-associated gene 51 (TDAG51)], cytokeratin 15 (CK15) and cytokeratin (CK19). RESULTS: All but one MAC was negative for BerEP4 and all morpheaform BCC expressed BerEP4. Sixteen out of 21 DTE were immunoreactive for BerEP4. All 21 DTE were PHLDA1 positive and all 17 morpheaform BCC were PHLDA1 negative. MAC showed a mixed staining pattern for PHLDA1. CK15 was expressed in 20/21 DTE, whereas the majority of cases of MAC and morpheaform BCC were CK15 negative. CK19 stained more MAC than DTE and morpheaform BCC. CONCLUSIONS: BerEP4 differentiates between MAC and morpheaform BCC but not between MAC and DTE whereas PHLDA1 differentiates between DTE and morpheaform BCC but shows variable staining in MAC. CK15 and CK19 are helpful adjuncts in the differential diagnosis of sclerosing adnexal neoplasms but are second in line to BerEP4 and PHLDA1. We propose an algorithm for the immunohistochemical work-up of sclerosing adnexal neoplasms.

The concept of the onychodermis (specialized nail mesenchyme): an embryological assessment and a comparative analysis with the hair follicle.

BACKGROUND: Recently, an intriguing concept was introduced into the literature that defines the area underlying the nail bed as a specific mesenchymal substructure unique to the nail organ. It has been termed onychodermis. The onychodermis expresses CD10 with remarkable specificity. Herein, we compare adult and fetal human hair follicles with fetal nail organs in an attempt to draw analogies for the mesenchyme associated with both adnexal structures. METHODS: We examined immunohistochemically samples from adult and fetal hair follicles for the expression of CD10, CD34 and the mesenchymal stem cell marker nestin and compared the antigen profile with that of the fetal nail organ. RESULTS: The CD10-positive/CD34-negative onychodermis is prominently visible at the end of the second trimester. A corresponding follicular structure was not identified, either in the adult or in the developing hair follicle. Nestin staining does not define the onychodermis. CONCLUSIONS: The concept of the onychodermis is equally valid in the developing nail organ where it is also defined by its expression for CD10. Its function may be related to the anchorage of the overlying nail bed but may also involve a more dynamic role in the induction of hard keratins in the latter, contributing to the formation of the nail plate.

The ventral proximal nail fold: stem cell niche of the nail and equivalent to the follicular bulge--a study on developing human skin.

BACKGROUND: Although the bulge is well characterized as a stem cell niche of the hair follicle, comparatively little is known about the location of stem cells in the nail. Herein, we describe the spatiotemporal expression pattern of six stem cell markers in the developing human nail and compared it with the embryonic and fetal human hair follicle. The areas of proliferative activity were additionally examined using labeling with Ki-67. METHODS: We examined immunohistochemically samples from embryonic and fetal human nail, hair and skin for the expression of cytokeratin 15 (CK15, two clones), cytokeratin 19 (CK19), PHLDA1, CD200, nestin and Ki-67 using standard techniques. RESULTS: CK15 (clone LHK15), CK19 and PHLDA1 are negative in the nail and hair matrix but positive in the ventral proximal nail fold and in the follicular bulge. Over the course of embryogenesis they display a highly specific spatiotemporal expression pattern both in the nail and in the hair follicle. CONCLUSIONS: We propose that at least during embryogenesis the proximal ventral nail fold represents the niche for the nail stem cells. In contrast to animal experiments, autoradiographic pulse-chasing studies cannot be performed in human, and immunohistochemical studies are a valid alternative although they have their limitations. Further studies on adult human nail units are suggested.

Follicular stem cell marker PHLDA1 (TDAG51) is superior to cytokeratin-20 in differentiating between trichoepithelioma and basal cell carcinoma in small biopsy specimens.

BACKGROUND: Biopsies submitted to dermatopathologists are becoming increasingly smaller in size and thus the available diagnostic material is reduced. The distinction between trichoepithelioma and basal cell carcinoma remains challenging, particularly if tissue is limited. Merkel cells, which can be highlighted by means of cytokeratin-20 (CK20) immunostaining, are used as a surrogate marker for the diagnosis of trichoepithelioma, as Merkel cells commonly colonize trichoepithelioma but are generally lacking in basal cell carcinomas. In the current study, we examined the expression of a recently characterized follicular stem cell marker, PHLDA1 (pleckstrin homology-like domain, family A, member 1), also known as TDAG51 (T-cell death-associated gene 51). METHODS: Using standard immunohistochemical techniques, we examined 19 trichoepitheliomas and 11 basal cell carcinomas for the expression of PHLDA1 and compared it with CK20 expression. RESULTS: All 19 trichoepitheliomas were immunoreactive for PHLDA1 and all 11 basal cell carcinomas lacked PHLDA1 expression. Two of eleven basal cell carcinomas harbored CK20-positive Merkel cells. Three trichoepitheliomas lacked secondary CK20-positive cells. CONCLUSIONS: Our results suggest that PHLDA1 represents a practical and easily used tool that can be applied to the differentiation of trichoepithelioma and basal cell carcinoma in small biopsy specimens. Rather than searching for CK20-positive Merkel cells, assessing PHLDA1 expression allows the differential diagnosis between trichoepithelioma and basal cell carcinoma to be solved at scanning magnification.

Expression of embryonic stem cell markers SOX2 and nestin in dermatofibrosarcoma protuberans and dermatofibroma.

BACKGROUND: Dermatofibrosarcoma protuberans (DFSP) was recently proposed to originate from a nestin-positive stem cell. In postnatal skin, nestin and another embryonic stem cell marker, SOX2, display a similar expression pattern with immunoreactivity in the hair follicle papilla and scattered cells of the perifollicular connective tissue sheath. The distribution pattern differs only in early embryogenesis, when nestin but not SOX2 is also expressed throughout the entire interfollicular dermis. We speculated that DFSP would not only be nestin-positive but also SOX2-positive. METHODS: With appropriately reacting external and internal controls, we examined 24 examples of DFSP for SOX2 and nestin. For comparison, we included 10 dermatofibromas (DFs). RESULTS: All 24 cases of DFSP were immunoreactive for nestin but negative for SOX2. The DFs were both nestin-negative and SOX2-negative. CONCLUSIONS: The observed staining pattern may indicate that DFSP derives from a subtype of nestin-immunoreactive mesenchymal stem cell that is different from the nestin- and SOX2-positive cell population of the perifollicular mesenchyme. Alternatively, nestin expression in DFSP may represent a recapitulation of the staining pattern in early embryogenesis without necessarily indicating that the nestin-positive cells represent stem cells. Also, DFSP may derive from hair follicle-associated mesenchymal stem cells that have lost their SOX2 expression.

Merkel cell carcinoma in a patient with autoimmune hepatitis.

Merkel cell carcinoma (MCC) has been shown to have a higher incidence in many etiologically distinct immunosuppressed populations. We report a case of aggressive MCC diagnosed in a man with autoimmune hepatitis who was treated with immunosuppressive therapy for more than 30 years.