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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. (Arch Pathol Lab Med. 2017;141:1490-1502; doi: 10.5858/arpa.2017-0222-RA), Basal cell carcinoma (BCC) is the most common malignant neoplasm, with an estimated overall lifetime risk of 30% in the United States. (1,2) Although BCC may cause extensive local tissue [...]

This study sought to evaluate a cohort of patients with verrucous carcinoma of the foot with special focus on 5 cases of locally recurrent tumors despite negative margins. Nineteen cases of verrucous carcinoma of the foot were identified through the University of Michigan (Ann Arbor, Michigan) pathology database from 1995 to 2019 and were included in demographic and clinical presentation analyses. Sixteen cases were treated at the University of Michigan and are included in the treatment analyses. A review of medical records was conducted to characterize clinical, surgical, and pathologic features. Recurrent cases were found to have a predilection for nonglabrous skin of the foot and great toe. Otherwise, there was little to differentiate outcomes between recurrent and nonrecurrent groups based on demographic, clinical, surgical, or histopathologic data. Recurrent tumors regrew locally and were not associated with histologic progression to conventional squamous cell carcinoma. Verrucous carcinoma of the nonglabrous surface of the foot should have a higher suspicion for possible local recurrence. Recurrence occurs within months of treatment, deserves early biopsy, and warrants aggressive re-treatment. Future directions should include greater examination of pathologic features and genetic markers to improve management of verrucous carcinoma of the foot. [ABSTRACT FROM AUTHOR]

Aims: Tumours of the cutaneous adnexa arise from, or differentiate towards, structures in normal skin such as hair follicles, sweat ducts/glands, sebaceous glands or a combination of these elements. This class of neoplasms includes benign tumours and highly aggressive carcinomas. Adnexal tumours often present as solitary sporadic lesions, but can herald the presence of an inherited tumour syndrome such as Muir–Torre syndrome, Cowden syndrome or CYLD cutaneous syndrome. In contrast to squamous cell carcinoma and basal cell carcinoma, molecular changes in adnexal neoplasia have been poorly characterised and there are few published reviews on the current state of knowledge. Methods and results: We reviewed findings in peer‐reviewed literature on molecular investigations of cutaneous adnexal tumours published to June 2021. Conclusions: Recent discoveries have revealed diverse oncogenic drivers and tumour suppressor alterations in this class of tumours, implicating pathways including Ras/MAPK, PI3K, YAP/TAZ, beta‐catenin and nuclear factor kappa B (NF‐κB). These observations have identified novel markers, such as NUT for poroma and porocarcinoma and PLAG1 for mixed tumours. Here, we provide a comprehensive overview and update of the molecular findings associated with adnexal tumours of the skin. [ABSTRACT FROM AUTHOR]

Spitzoid melanocytic lesions encompass a spectrum from benign Spitz nevi to malignant spitzoid melanomas. Spitzoid melanocytic neoplasms have significant morphologic and molecular differences from conventional melanocytic lesions, and prediction of biologic behavior and metastatic risk may be difficult. Most challenging is the atypical Spitz tumor, a borderline spitzoid melanocytic lesion of uncertain malignant potential that has overlapping histologic features with conventional Spitz nevus and spitzoid melanoma. Atypical Spitz tumors involve the sentinel lymph nodes at a greater frequency than conventional melanoma and frequently harbor chromosomal copy number changes, yet most cases follow an indolent course. Herein we review the clinical, microscopic, and molecular features of atypical Spitz tumors, including recent molecular advances, including the potential prognostic significance of chromosomal abnormalities, such as homozygous CDKN2A loss. (Arch Pathol Lab Med. 2015; 139:1263-1270; doi: 10.5858/arpa.2015-0207-RA), Since they were first described by Sophie Spitz in 1948, (1) spitzoid melanocytic lesions have proven to be an enduring challenge for both clinicians and pathologists, given the difficulty in [...]

Abstract Background Apart from neoplastic processes, chronic disfiguring and destructive diseases of the mandible are uncommon. Case Presentation We report, perhaps for the first time, the simultaneous occurrence of two such conditions in one patient, in a case that emphasizes the importance of bone biopsy in establishing the correct diagnosis. Florid cemento-osseous dysplasia (FCOD) is a chronic, disfiguring condition of the maxillofacial region. This relatively benign disease is primarily observed in middle-aged women of African ancestry. Cervicofacial actinomycosis is an uncommon and progressive infection caused by bacilli of the Actinomyces genus that typically involves intraoral soft tissues but may also involve bone. The accurate diagnosis of actinomycosis is critical for successful treatment. A diagnosis of osteomyelitis caused by Actinomyces bacteria was diagnosed by bone biopsy in a 53 year-old African-American woman with a longstanding history of FCOD after she presented with a new draining ulcer overlying the mandible. Conclusions Clinicians should be aware of the possibility of actinomycosis arising in the setting of FCOD, and the importance of bone biopsy and cultures in arriving at a definitive and timely diagnosis.

Follicle center lymphomas, including primary cutaneous follicle center lymphoma (PCFCL), may rarely show plasmacytic differentiation. Such cases can pose a diagnostic challenge and can be mistaken for other lymphomas that more commonly include plasma cells. Here, we report four cases of PCFCL and one case of systemic follicular lymphoma involving the skin with associated monotypic plasma cells, including the clinical, morphologic and immunophenotypic features. [ABSTRACT FROM AUTHOR]

Clear cell melanoma is a rare clear cell malignancy. Accurate diagnosis of clear cell melanoma requires integration of immunohistochemical and morphologic findings, with molecular studies to rule out clear cell sarcoma. The differential diagnosis includes melanoma, carcinoma, perivascular epithelioid cell tumor, and epidermotropic clear cell sarcoma. We use a case of a lesion on the helix of an 86-year-old man as an example. Histologic examination revealed an ulcerated clear cell malignant tumor. Tumor cell cytoplasm contained periodic acid-Schiff-positive, diastase-sensitive glycogen. Tumor cells showed positive labeling for S100, HMB-45, and Melan-A, and negative labeling for cytokeratins, p63, and smooth muscle actin. Molecular studies demonstrated BRAF V600E mutation, copy gains at the 6p25 (RREB1) and 11q13 (CCND1) loci, and absence of EWSR1-ATF1 fusion. These findings supported a diagnosis of clear cell melanoma. The rare pure clear cell morphology occurs due to accumulation of intracytoplasmic glycogen. We review the differential diagnosis of clear cell melanoma and describe the utility of immunohistochemical and molecular studies in confirming this diagnosis. (Arch Pathol Lab Med. 2014; 138:1328-1336; doi: 10.5858/arpa.2014-0307-CC), STUDY CASE Clear cell melanoma is a rare clear cell malignancy. Accurate diagnosis of clear cell melanoma requires integration of immunohistochemical and morphologic findings, with molecular studies to rule out [...]

Although multiple studies have assessed molecular changes in chronic atopic dermatitis (AD) lesions, little is known about the transition from acute to chronic disease stages, and the factors and mechanisms that shape chronic inflammatory activity. We sought to assess the global transcriptome changes that characterize the progression from acute to chronic stages of AD. We analyzed transcriptome changes in paired nonlesional skin, acute and chronic AD lesions from 11 patients and 38 healthy controls by RNA-sequencing, and conducted in vivo and histological assays to evaluate findings. Our data demonstrate that approximately 74% of the genes dysregulated in acute lesions remain or are further dysregulated in chronic lesions, whereas only 34% of the genes dysregulated in chronic lesions are altered already in the acute stage. Nonlesional AD skin exhibited enrichment of TNF, T H 1, T H 2, and T H 17 response genes. Acute lesions showed marked dendritic-cell signatures and a prominent enrichment of T H 1, T H 2, and T H 17 responses, along with increased IL-36 and thymic stromal lymphopoietin expression, which were further heightened in chronic lesions. In addition, genes involved in skin barrier repair, keratinocyte proliferation, wound healing, and negative regulation of T-cell activation showed a significant dysregulation in the chronic versus acute comparison. Furthermore, our data show progressive changes in vasculature and maturation of dendritic-cell subsets with chronicity, with FOXK1 acting as immune regulator. Our results show that the changes accompanying the transition from nonlesional to acute to chronic inflammation in AD are quantitative rather than qualitative, with chronic AD having heightened T H 2, T H 1, T H 17, and IL36 responses and skin barrier repair mechanisms. These findings provide novel insights and highlight underappreciated pathways in AD pathogenesis that may be amenable to therapeutic targeting. [ABSTRACT FROM AUTHOR]

Pigmented epithelioid melanocytoma (PEM) represents a group of rare, heavily pigmented melanocytic tumors encompassing lesions previously designated as "animal‐type melanomas" and "epithelioid blue nevi." Despite the association of multiple such tumors in the setting of Carney complex, most cases of PEM occur spontaneously as solitary neoplasms in otherwise healthy patients. PEM may arise in both children and adults, and has a known propensity to spread to the regional lymph nodes. Despite this latter finding, recurrence at the biopsy site or spread beyond the lymph node basin is exceptionally uncommon. Although the molecular basis for PEM continues to be characterized, findings to date suggest that this category of melanocytic neoplasia has genetic alterations distinct from those seen in common nevi, dysplastic nevi, Spitz nevi, and melanoma. Herein, we present an in‐depth clinical, histopathologic, and molecular analysis of a case of PEM occurring on the scalp of a young African American girl found to have a novel NTRK3‐SCAPER gene fusion. [ABSTRACT FROM AUTHOR]