Anti-cytokeratin 20 staining of Merkel cells helps differentiate basaloid proliferations overlying dermatofibromas from basal cell carcinoma

INSM1 Is More Sensitive and Interpretable than Conventional Immunohistochemical Stains Used to Diagnose Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is an extremely aggressive skin cancer that must be distinguished from other basaloid cutaneous neoplasms that have different treatments and prognoses. This is sometimes challenging in small shave specimens, crushed samples, lymph nodes, and core needle biopsies. Insulinoma-associated protein 1 (INSM1) immunohistochemistry is a sensitive nuclear marker of neuroendocrine differentiation. INSM1 staining was performed on 56 MCC (47 primary tumors, 9 nodal metastases), 50 skin control cases that included basal cell carcinomas, basaloid squamous cell carcinomas, Bowen disease, sebaceous neoplasms, melanoma, and B-cell lymphomas, and 28 lymph node control cases that included metastatic neuroendocrine neoplasms, melanomas, squamous cell carcinomas, lymphomas, and adenocarcinomas. Percent of staining nuclei (0, <25%, 25% to 50%, 50% to 75%, >75%) and intensity (weak, moderate, strong) were recorded for each sample. All 56 MCC expressed INSM1. By comparison, synaptophysin, CK20, and chromogranin were expressed in 96%, 92%, and 32% of MCC, respectively. While the 3 conventional markers showed significant variability in staining intensity and distribution, INSM1 stained >75% tumor nuclei in 89% of MCC and 50% to 75% of tumor nuclei in 11%. Staining intensity was strong in 85% and moderate in 15%. None of the 50 cutaneous basaloid non-MCC neoplasms in the control group stained with INSM1, and among the lymph node controls 5 of 5 neuroendocrine neoplasms expressed INSM1, confirming that INSM1 staining cannot distinguish MCC from metastatic extracutaneous neuroendocrine carcinoma. INSM1 holds promise as a neuroendocrine marker that can distinguish MCC from its mimickers in the skin and improve detection of sentinel lymph node metastases.

Follicular induction and CK20+ Merkel cells overlying cutaneous focal mucinosis

BACKGROUND

Cutaneous focal mucinosis (CFM) or focal dermal mucinosis is a benign reactive process categorized as a primary mucinosis. Skin biopsy is essential for diagnosis, as the clinical appearance is often non-specific. Follicular induction is a phenomenon whereby the epidermis is induced by an underlying process to form primitive or mature hair follicles, and is commonly seen overlying dermatofibromas. Follicular induction has been rarely described in CFM.

METHODS

We performed a retrospective histological review of lesions of CFM confirmed by skin biopsy from 2010 to 2015 in our department.

RESULTS

We found that 11% (11/98) of CFM lesions showed follicular induction. Cytokeratin 20 (CK20) immunostaining was performed on all 11 of these biopsies that showed follicular induction and highlighted an increased density of CK20+ Merkel cells within the basaloid epidermal proliferations.

CONCLUSION

As superficial basal cell carcinomas (BCC) often show a mucinous stroma around the basaloid islands, CFM with follicular induction may closely mimic a BCC histologically, particularly in superficial shave biopsies. Therefore, it is important that dermatopathologists be aware of this phenomenon. Furthermore, CK20+ staining within the basaloid epithelial proliferations may be helpful in differentiating CFM with follicular induction from a BCC.

CD34 and BerEP4 Are Helpful to Distinguish Basaloid Tricholemmoma From Basal Cell Carcinoma

Tricholemmoma, a benign follicular neoplasm with outer root sheath differentiation, typically comprises clear or pale cells, and when multiple is pathognomic of Cowden's syndrome. The tumor is probably underrecognized and in basaloid examples can be difficult to distinguish from basal cell carcinoma (BCC). We studied 55 tricholemmomas (including 15 basaloid cases) and compared immunohistochemical profile with nodular BCC from our archives. Basaloid and non-basaloid tricholemmomas had similar staining characteristics. BerEP4 was focally positive (range 10%-20%) in only 3/39 (7.7%) tricholemmomas compared with widespread positivity in BCC (90.8%, 139 of 151 cases with ≥50% tumor area stained). CD34 was expressed, usually focally (median 20%, range 10%-90%), in 52/53 (98.1%) tricholemmomas and was negative in all 21 BCCs stained. EMA staining lacked sensitivity or specificity in differentiating tricholemmoma from BCC. Five or more Merkel cells were found in 7/17 (40.1%) tricholemmomas and 1/23 (4.3%) nodular BCCs studied. In summary, immunohistochemistry is helpful in distinction between tricholemmoma, including difficult basaloid examples (BerEP4 negative or focal, CD34 positive) compared with BCC (BerEP4 widespread in most cases, CD34 negative). The presence of 5 or more Merkel cells is a relatively specific but not a particularly sensitive discriminator.

Merkel cells in extraocular sebaceous carcinoma

INTRODUCTION

Mature sebaceous glands do not contain Merkel cells. Neither do sebaceous tumors in the vast majority of cases. Recently, however, it was showed that rare sebaceous adenomas with a carcinoid-like or labyrinthine pattern can contain intratumoral Merkel cells. Our purpose in this study is to examine for the presence of Merkel cells in extraocular sebaceous carcinomas.

METHODS

Nineteen cases of extraocular sebaceous carcinoma were retrospectively studied with cytokeratin 20.

RESULTS

One out of 19 cases (5.3%) contained Merkel cells in the basal layers of the tumoral nests of a sebaceous carcinoma from the cheek of a 76-year-old woman.

CONCLUSIONS

Merkel cells are rarely evident in extraocular sebaceous carcinoma, and therefore, their evidence does not exclude this diagnosis.

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.

Challenges in the diagnosis of cutaneous adnexal tumours

The diagnosis of cutaneous adnexal neoplasms, a heterogeneous group of entities, is often perceived by practising pathologists as challenging. A systematic approach to diagnosis is necessary for classification of these lesions, which establishes the tumour differentiation (follicular, sebaceous, sweat gland or apocrine) and evaluates histological features differentiating between benign and malignant entities. Consideration of clinical history is a necessary adjunct in evaluation of the adnexal neoplasm, as characteristic anatomical sites are described for many adnexal lesions. In some instances, immunohistochemical studies may also be employed to aid the diagnosis. The differential diagnosis between primary cutaneous adnexal neoplasms and cutaneous metastases from visceral tumours may also be difficult. Clinical, radiological, histological and immunohistochemical characteristics will be further discussed, considering that the correct diagnosis has a significant impact on the patient's management and prognosis.

Primitive follicular induction in molluscum contagiosum

BACKGROUND

Molluscum contagiosum (MC) is the commonest human poxvirus infection. Follicular induction has rarely been observed in the epidermis surrounding lesions of MC. A virus-induced localized proliferation of germinative/stem cells of the folliculosebaceous-apocrine unit has been suggested as the underlying cause, however few reports of this peculiar phenomenon exist in the literature and the mechanisms involved in this proliferation require further study.

METHODS

We prospectively collected MC cases showing multifocal areas of primitive follicular induction involving the adjacent undersurface epidermis. Immunohistochemical expression of BerEP4, PHLDA1 and cytokeratin 20 (CK20) was evaluated in the basaloid germs surrounding the lesions. For PHLDA1, we used epidermal melanocytes as a positive internal control. For BerEP4, we employed a basal cell carcinoma (BCC) and for CK20, colon as positive external controls. An incubation without the primary antibody functioned as an external negative control.

RESULTS

All the cases studied showed an intense positive staining of the basaloid buds with BerEP4 and weaker stain for PHLDA1. CK20 showed the presence of scattered Merkel cells within the induced epidermal basaloid proliferations favoring their reactive origin.

DISCUSSION

The pathogenetic mechanisms behind the development of these microscopic features and the link between follicular induction and poxvirus infection are explored. Awareness of this unusual phenomenon by dermatopathologists will be helpful in avoiding a misdiagnosis of a superficial BCC in such cases.

CONCLUSIONS

BerEP4 and PHLDA1 were consistently expressed in the areas of primitive follicular induction surrounding lesions of MC. CK 20 stained the Merkel cells present in the basaloid buds. All these findings support the reactive origin of this phenomenon, which we believe is most probably viral-induced.

Scar and induction of follicles: an association worthy of greater awareness

Alterations in the dermal connective tissue can sometimes induce epidermal changes with adnexal differentiation. Typically associated with dermatofibromas, such changes can also be seen in a wide range of reactive and neoplastic conditions. Scar is sometimes listed as an underlying cause of follicular induction, but this association seems to be poorly recognized and not widely discussed in the literature. In this article, the authors illustrate the spectrum of follicular induction, which may be associated with a dermal scar emphasizing on patterns, which can be mistaken for a basal cell carcinoma.

Immunohistochemistry panel for differential diagnosis of Basal cell carcinoma and trichoblastoma

Introduction:

Basal cell carcinoma (BCC) is the most common malignant neoplasm in the skin and is considered to have a low degree of malignancy. BCC is invasive but rarely metastatic and originates in hair follicle-derived cells or interfollicular zones of the epidermis. Trichoblastoma (TB) is an infrequent benign skin neoplasm that differentiates toward follicular germinative cells. Both of these cutaneous lesions comprise nests of basaloid cells, and because the differential diagnosis is hard to obtain between them histologically due to their similarity, the correct diagnosis must be established.

Materials and Methods:

The sample size of this descriptive study consisted of 20 cases: 10 paraffin-embedded tissues that were diagnosed with carcinoma of solid basal cells with follicular differentiation and 10 TB tissues. The diagnosis of all samples was confirmed morphologically with hematoxylin and eosin. One-micron-thick sections were cut from each sample and analyzed semiquantitatively by immunohistochemistry (IHC). Differences in staining between BCC and TB were analyzed by Chi-square test.

Results:

Two of 10 TB cases were positive for Ki-67 versus 10 of 10 BCC samples. Cytokeratins 6 was expressed in 1 of 10 TB samples and in all BCC tissues. Staining with clone 34BE12 generated signals in all lesions at various intensities.

Conclusion:

The diagnosis between TBs and BCCs must be made histologically, because the treatment of BCC is radical and can compromise aesthetics and function, even for experienced pathologists. Because their morphological diagnosis is difficult, the histopathology results must be supported by an IHC panel.

Follicular induction in a case of molluscum contagiosum: possible link with secondary anetoderma-like changes?

Molluscum contagiosum (MC) can rarely show follicular neogenesis as a result of proliferation of virus-infected basal cells. We report a case of molluscum contagiosum showing multifocal areas of primitive follicular induction involving the adjacent surface epidermis. The underlying dermis showed histological features suggestive of secondary anetoderma. The pathogenetic mechanisms behind development of these microscopic features and the putative link between follicular induction and secondary anetoderma are explored. Awareness of this unusual phenomenon will be helpful in avoiding a misdiagnosis of a superficial basal cell (trichoblastic) carcinoma in such cases.

Does the panel of cytokeratin 20 and androgen receptor antibodies differentiate desmoplastic trichoepithelioma from morpheaform/infiltrative basal cell carcinoma?

BACKGROUND

Evaluation of androgen receptor (AR) and cytokeratin 20 (CK20) expression can aid in distinguishing between conventional basal cell carcinoma (characteristically AR+, CK20-) and trichoepithelioma (frequently AR-, CK20+). Within these two groups of tumors, morpheaform/infiltrative basal cell carcinoma (mBCC) and desmoplastic trichoepithelioma (DTE) are particularly challenging to differentiate both clinically and histologically. We investigated whether AR and CK20 immunostains may distinguish between mBCC and DTE.

METHODS

Immunohistochemistry for AR and CK20 was performed on 15 DTEs and 31 mBCCs. Any immunoreactivity within the tumor for AR or CK20 was considered positive.

RESULTS

AR expression was seen in 13% (2/15) of DTE and 65% (20/31) of mBCC cases (chi-square p = 0.0011). CK20-positive Mërkel cells were identified in 100% (15/15) of DTE and 3% (1/31) of mBCC (chi-square p < 0.0001). The expected pattern of AR-, CK20+ immunophenotype was present in 87% (13/15) of DTE cases. In mBCC, 61% (19/31) was AR+, CK20-. No DTE was AR+, CK20- and no mBCC was AR-, CK20+.

CONCLUSIONS

Immunohistochemical stains for AR and CK20 are useful to differentiate DTE from mBCC. The AR-, CK20+ immunophenotype is sensitive (87%) and specific for DTE (100%). The AR+, CK20- immunophenotype is specific (100%) and moderately sensitive (61%) for mBCC.

Merkel cells

Merkel cells are post-mitotic cells scattered throughout the epidermis of vertebrates. They are particularly interesting because of the close connections that they develop with sensory nerve endings and the number of peptides they can secrete. These features suggest that they may make an important contribution to skin homeostasis and cutaneous nerve development. However, these cells remain mysterious because they are difficult to study. They have not been successfully cultured and cannot be isolated, severely hampering molecular biology and functional analysis. Merkel cells probably originate in the neural crest of avians and mammalians, and their "spontaneous" appearance in the epidermis may be caused by a neuron-independent epidermal differentiation process. Their functions are still unclear: they take part in mechanoreception or at least interact with neurons, but little is known about their interactions with other epidermal cells. This review provides a new look at these least-known cells of the skin. The numerous peptides they synthesize and release may allow them to communicate with many cells other than neurons, and it is plausible that Merkel cells play a key role in skin physiology and physiopathology.

Merkel Cell Tumor in a Trichilemmal Cyst: Collision or Association?

An 86-year-old white male presented with an erythematous, painless, slowly growing, and firm left thigh nodule. Histologic examination revealed a dermal proliferation of monomorphous cells arranged in trabeculae, nests, and sheets with an infiltrative growth pattern. The cells had a high nuclear-cytoplasmic ratio, finely granular nuclear chromatin, and nuclear molding. Numerous mitotic figures, apoptotic cells, and individual cell necrosis were present; lymphovascular invasion was identified. The tumor was attached, demonstrating pagetoid intraepithelial migration, to a follicular cyst lined by squamous epithelium, lacking a granular cell layer and filled with compact keratinous content, diagnostic of trichilemmal cyst. Immunohistochemical study revealed that tumor cells expressed pan-cytokeratin (CK), chromogranin, synaptophysin, neuron-specific enolase, and CK20 (dotlike staining pattern), thus supporting the diagnosis of Merkel cell carcinoma. The association of Merkel cell carcinoma with a cyst is an exceptionally rare occurrence. As a result of the prominent involvement of the cyst wall by tumor cells, we favor that in this case carcinoma arose in the trichilemmal cyst rather than being a collision tumor. This hypothesis is also supported by the recent observation that Merkel cells are frequently present within normal hair follicles, especially in the isthmic portion that corresponds with the area of origin of the trichilemmal cyst.

Expression of Androgen Receptor by Fibroepithelioma of Pinkus: Evidence Supporting Classification as a Basal Cell Carcinoma Variant?

The classification of fibroepithelioma of Pinkus as basal cell carcinoma or trichoblastoma remains controversial. Immunohistochemical stains for androgen receptor may be useful in differentiating basal cell carcinoma from trichoepithelioma or trichoblastoma. We studied androgen receptor expression in 13 fibroepitheliomas of Pinkus, 11 basal cell carcinomas, 12 trichoepitheliomas, and 3 trichoblastomas. Androgen receptor expression was present in 77% (10/13) of fibroepitheliomas of Pinkus, 73% (8/11) of basal cell carcinomas, 17% (2/12) of trichoepitheliomas, and 0% (0/3) of trichoblastomas. Androgen receptor expression was significantly higher in fibroepitheliomas of Pinkus compared with trichoepitheliomas and trichoblastomas (P = .0007), but not basal cell carcinoma (P = 1.00). Tumor-associated Merkel cells, a feature of benign follicular tumors, was identified by cytokeratin 20 stains. Merkel cells were identified in 85% (11/13) of fibroepitheliomas of Pinkus, 27% (3/11) of basal cell carcinoma cases, and 73% (11/15) of benign follicular tumors. Cytokeratin 20 expression was significantly higher in fibroepithelioma of Pinkus and benign follicular tumors compared with basal cell carcinomas (P = 0.0111 and P = 0.025, respectively). No significant difference was found between fibroepitheliomas of Pinkus and trichoepitheliomas and trichoblastomas (P = 1.00). Similar to basal cell carcinomas, fibroepitheliomas of Pinkus express androgen receptors, potentially supporting classification as a basal cell carcinoma. Conversely, fibroepithelioma of Pinkus demonstrates retention of Merkel cells, a feature of benign follicular tumors. Immunophenotypic evidence for the classification of fibroepithelioma of Pinkus remains inconclusive. In small, partial biopsy specimens, coexpression of androgen receptor and cytokeratin 20 may aid in the diagnosis of fibroepithelioma of Pinkus.

Skin adnexal neoplasms--part 1: an approach to tumours of the pilosebaceous unit

Skin adnexal neoplasms comprise a wide spectrum of benign and malignant tumours that exhibit morphological differentiation towards one or more types of adnexal structures found in normal skin. Most adnexal neoplasms are relatively uncommonly encountered in routine practice, and pathologists can recognise a limited number of frequently encountered tumours. In this review, the first of two, the normal histology of the skin adnexal structures is reviewed, and the histological features of selected but important benign and malignant tumours and tumour-like lesions of pilosebaceous origin discussed, with emphasis on the diagnostic approach and pitfalls in histological diagnosis.