Merkel Cell Carcinoma (Primary Neuroendocrine Carcinoma of Skin) Mimicking Basal Cell Carcinoma With Review of Different Histopathologic Features

Merkel Cell Carcinoma of the Upper Eye Lid with Atypical Clinical Appearance

Merkel cell carcinoma (MCC) is a rare aggressive neuroendocrine skin tumor that occurs mainly in the sun-exposed head and neck region, but rarely in the eyelid region. Early lymphogenic spread often leads to locoregional metastases, which is why early diagnosis is crucial. Classically, periocular MCC presents as a reddish-livid nodule in elderly patients, a visual diagnosis. However, given its low incidence and variable appearance, diagnosis can also be challenging. In both cases presented here, the MCC presented as a skin-colored swelling. In patient 1, the tumor showed a partially deep subaponeurotic localization and mimicked a B-cell lymphoma histopathologically, whereas in patient 2 it imitated a diffuse chalazion clinically. After immunohistochemical characterization and exclusion of metastases, the initial clinically benign appearing lesions in both patients were classified as CK20 negative MCC. The extensive upper eyelid defects were reconstructed by Cutler-Beard plastic surgery, a particular challenge in patient 1 given the oculus unicus situation. Our two cases demonstrate that Merkel cell carcinomas not only manifest as deep red cherry-shaped tumors, but can be skin-colored and mimic benign changes when atypical in location or infiltration pattern.

Reproducible Histopathologic Features in Cases of Basal Cell Carcinoma With Neuroendocrine Expression: A Clinicopathologic Study of 24 Cases With a Potential Diagnostic Pitfall

ABSTRACT

Basal cell carcinomas (BCCs) are common malignancies that usually show clear histomorphologic features, but in certain instances, it can display different patterns of differentiation leading to potential diagnostic confusion. BCCs with neuroendocrine differentiation/expression have been mentioned only briefly in the literature. In this study, we present cases of BCCs with neuroendocrine differentiation/expression that demonstrate reproducible histopathological features. Twenty-four cases were included in the study. All tumors showed conventional histopathologic features that are seen in BCCs, but in addition, all the tumors showed large, hyperchromatic, pleomorphic, mononuclear, and multinucleate cells with intracytoplasmic inclusions and intranuclear cytoplasmic invaginations, with rare cases showing stippled nuclei (salt-and-pepper appearance). These histologic features were somewhat concerning for a neuroendocrine carcinoma; thus, immunohistochemistry studies were performed in all cases at the time of diagnosis. By immunohistochemistry, all tumors showed expression of neuroendocrine markers. CD56 was expressed in all cases 24/24, chromogranin was positive in 17/24 cases, and synaptophysin 8/24 was positive in cases. This study confirms a subset of histopathologic features that are present in cases of BCC that are associated with neuroendocrine expression that can potentially be interpreted differently and can create a diagnostic pitfall. Neuroendocrine expression in BCCs is yet uncertain, and further studies are required to fully understand this phenomenon. To avoid diagnostic pitfalls, dermatopathologists must be aware of these unusual histopathologic features and aberrant immunostaining in such tumors; hence, it is advised to perform a thorough histologic inspection.

Neuroendocrine Differentiation of Skin Tumors: A Comprehensive Review

Neuroendocrine differentiation is characterized by endocrine and neuronal features with prominent dense secretory granules and neuropeptides. Neuroendocrine differentiation of skin tumors is of unknown clinical significance. Nonetheless, the acknowledgment of this line of differentiation is important to prevent diagnostic pitfalls and subsequent inappropriate management. This review aims at summarizing the skin neoplasms that can express neuroendocrine markers.

Intraepidermal Merkel Cell Carcinoma Mimicking Melanoma in Situ: A Case Report

Merkel cell carcinoma (MCC) is an uncommon, but aggressive neoplasm with neuroendocrine differentiation that occurs on sun-damaged skin of the elderly. Because its clinical presentation is usually nonspecific, the diagnosis is often made after histopathologic evaluation. Most cases are intradermal. Epidermal involvement is uncommon, whereas MCC limited to the epidermis is extremely rare. Here, we describe a case of MCC in an 88-year-old man with an extraordinary histopathologic presentation, namely nested intraepidermal proliferation of neoplastic cells highly resembling melanoma in situ.

Metastatic Basal Cell Carcinoma of the Skin: A Comprehensive Literature Review, Including Advances in Molecular Therapeutics

Basal cell carcinoma (BCC) of the skin is the most common type of malignant human tumor. In Europe, the incidence of BCC ranges from 44.6 to 128 cases per 100,000 inhabitants annually, whereas in the United States, the yearly incidence rate ranges between 500 and 1500. The global incidence has been calculated to be as high as 10 million cases of BCC per year. There are 2 main clinical patterns of BCC-the familial BCC in basal cell nevus syndrome and sporadic BCC. The etiology of cutaneous BCC is usually the result of the interaction between solar ultraviolet radiation and genetic factors. Somatic or germline mutations in the effector components of the hedgehog signaling pathway (ie, PTCH1, PTCH2, SMO or SUFU genes) are responsible for ∼90% of the cases of both sporadic and familial BCC, all causing a constitutive activation of the hedgehog pathway. Cutaneous BCC very rarely metastasizes, and diagnosis in metastatic sites can be very difficult. Metastatic BCC has weakly effective therapeutic options with a poor prognosis until few years ago. In 2012, small-molecule therapies, involving inactivation of the hedgehog signaling pathway, and capable of reducing tumor growth and progression have been introduced into clinical practice for advanced (locally advanced or metastatic) BCC. We performed a comprehensive literature review on metastatic BCC and found at least 915 cases reported to date. In addition, we extensively discussed the differential diagnosis of metastatic BCC, and outlined the advances in clinical therapeutics involving these small molecules.

Metastatic Cutaneous Basal Cell Carcinoma: Report of 2 Cases Preceding the Hedgehog Pathway Antagonists Era

Basal cell carcinoma (BCC) of the skin is the most common type of malignant human tumor. However, metastatic BCC is a very rare event with weakly effective therapeutic options and a poor prognosis, until a few years ago. In 2012, small-molecule therapies, capable of inactivating the hedgehog signaling pathway and thus reducing tumor growth and progression, were introduced into clinical practice for the treatment of patients with advanced BCC. We present retrospectively 2 personal cases of metastatic BCC of the skin, from the premolecular therapy era, from primary tumors that arose years before in the head and neck area. The former case occurred in a 45-year-old woman with a history of recurrent BCC of the retroauricular skin who eventually died due to diffuse metastatic spread. The latter case concerned a 70-year-old man also with a history of recurrent BCC of the nasal-perinasal skin who developed multiple subcutaneous and lymph node metastases in the neck. In both cases, the diagnoses were based on biopsies of the metastatic sites. The first patient died 5 months after the diagnosis of metastatic disease, while the second was alive and disease-free 2 years after neck lymph node dissection and external radiation therapy, and then lost to follow-up. We extensively discuss several tumor entities with basal or basaloid features that may enter the differential diagnosis with BCC in metastatic sites. In addition, we briefly summarize the advances in clinical therapeutics using small molecules, which are now an integral part of the treatment of such advanced BCC cases.

Metastatic Basal Cell Carcinoma

OBJECTIVES

Diagnosis of metastatic basal cell carcinoma (BCC) remains challenging, in part due to its rarity. With the advent of molecularly targeted therapies, recognition of this entity is more important than ever.

METHODS

We identified 11 cases of metastatic BCC over a 13-year period. We analyzed these tumors in conjunction with their respective primary tumors by histomorphologic, immunohistochemical, and molecular genetic analyses.

RESULTS

We identified three morphologic patterns of metastasis in BCC. The most common (seven cases) was characterized by completely typical features of BCC. Two cases showed marked squamous differentiation within BCC. The final two cases showed exclusively features of a poorly differentiated carcinoma. One of these was definitively classified by molecular analysis, as both the primary and metastatic tumors harbored the same inactivating PTCH1 mutation.

CONCLUSIONS

This study illustrates multiple distinct morphologic patterns in metastatic BCC and highlights the utility of ancillary molecular testing for accurate diagnosis.

Merkel Cell Carcinoma: Current Issues Regarding Diagnosis, Management, and Emerging Treatment Strategies

Merkel cell carcinoma (MCC) is a rare but aggressive cutaneous tumor with a predilection for the head and neck of elderly Caucasian patients. Although much less common than melanoma, MCC has higher rates of sentinel lymph node involvement, local and regional recurrences, and mortality. The majority of MCC cases have been linked to the relatively newly discovered Merkel cell polyomavirus, which is a ubiquitous constituent of the skin flora. Recent discoveries regarding viral integration and carcinogenesis and the immunologic features of MCC have expanded the understanding of MCC. These discoveries have led to the development and application of emerging therapies such as somatostatin analogs, immune checkpoint inhibition, adoptive cell therapy, and other exciting possibilities for targeted therapy.

When biopsy alone is not enough for the diagnosis: angiomatous florid proliferation hiding a merkel cell carcinoma

Merkel cell carcinoma (MCC) is an aggressive tumor with an uncertain histogenesis typically arising on sun-damaged skin of the elderly. It has rarely been described in association with other tumors such as epithelial, melanocytic, and mesenchymal, but not vascular neoplasias. However, an exuberant vascular reaction is considered a common phenomenon in neuroendocrine neoplasms, where it can even obscure the proliferating cells and mimic a primary vascular neoplasia. A 47-year-old man was referred for the evaluation of a long-lasting reddish skin tumor located on the right buttock. After 2 punch biopsies, the patient underwent surgical excision of the lesion. Histological examination showed a dermal florid, benign vascular proliferation overlying some large deep coalescent nodules made up of monomorphous round cells with scant cytoplasm and a high mitotic activity. After the appropriate immunohistochemical stainings, a final diagnosis of hemangioma overlying a previously unrecognized MCC was rendered. Whether the angiomatous proliferation should be considered an exuberant reaction to the tumor, induced by an angiogenetic drive, or a true hemangioma is somewhat controversial. The main point is that such a neoplastiform angiomatous proliferation may represent a potential diagnostic pitfall, especially in limited specimens, and that an accurate clinicopathologic correlation is always needed. In our case, even if additional punch biopsies had been performed, the vascular proliferation would dominate the histological picture and an accurate diagnostic conclusion would probably not be reached due to the deep location of the MCC.

Pathophysiology of merkel cell

The objective of this review is to introduce Merkel cells (MCs), to provide a basic overview on the theoretical background of function, development and clinical importance of MCs. The origin of human MCs have been controversial. Some investigators believe that it is a neural crest derivate, whereas others have proposed that it is a differentiation product of the fetal epidermal keratinocytes. MCs are cells primarily localized in the epidermal basal layer of vertebrates and concentrated in touch-sensitive areas in glabrous, hairy skin and in some mucosa. In routine light microscopy, human MCs can hardly be identified. Cytokeratin 20 (CK20) is a reliable marker with highest degree of specificity. MCs can be also distinguished by electron microscopy. MC carcinoma (MCC) is an uncommon and often aggressive malignancy and found mainly in elderly patients. It occurs most frequently in the head and neck region. Diagnosis is based on typical histological presentation on hematoxylin and eosin (H and E) stained slides together with the results of immunohistochemistry. Histologically, MCC has been classified into three distinct subtypes: Trabecular, intermediate and small cell type.