Superficial plexiform schwannoma of the skin and subcutis: Clinicopathological study of 48 cases.

Aims: To study the clinicopathological characteristics of a large cohort of cutaneous plexiform schwannoma.

Methods And Results: A total of 48 cases of plexiform schwannoma were collected. Clinical and pathological features including age, location, location within the dermis, histology, immunohistochemical features, treatment and clinical follow-up were collected by reviewing glass slides or abstracted from the medical record.

Cytokeratin and Neuroendocrine Positivity in Cutaneous Small Blue Round Cell Tumor-Is It Always Merkel Cell Carcinoma?

We present a case of a 39-year-old woman initially diagnosed with Merkel cell carcinoma (MCC), a highly aggressive neuroendocrine carcinoma, due to the presence of cytokeratin and neuroendocrine marker expression. The tumor was dermal based, showing small round blue cells with fine chromatin, scant cytoplasm, and scattered mitotic figures arranged in sheets, small cohesive nests, and cords within sclerotic to edematous stroma. Provided immunohistochemical stains showed strong pancytokeratin expression coupled with perinuclear dot-like staining for cytokeratin 20 in a distinct regional distribution, predominantly in areas where the tumor cells formed cohesive nests and cords within sclerotic stroma.

Subungual Epidermoid Inclusions-A Series of 8 Cases and a Review of Literature.

Subungual epidermoid inclusions (SEI) are benign cystic lesions of the nail bed. To our knowledge, there has been only one case series describing SEI. We report eight cases of SEI.

MITF Pathway-Activated Cutaneous Neoplasms.

Over the past few years, several fusion genes have been reported in dermal-based tumors, resulting in the activation of the microphthalmia (MITF) signalling pathway and a melanocytic phenotype by immunohistochemistry. The best-studied example of these tumors is clear cell sarcoma, which rarely may present as a primary dermal tumor. These tumors are characterized by EWSR1 gene rearrangements, typically with ATF1 and less commonly CREB1.

Primary Cutaneous Neoplasm With Rhabdomyosarcomatous Differentiation and a Melanoma-Like Mutational Landscape.

Malignant melanoma (MM) is notorious for its wide range of morphologic variability. Rarely, MM may lose all melanocytic markers and adopt the morphologic and immunophenotypic characteristics of a different neoplasm in a process known as trans-differentiation (TMM). Distinguishing TMM from primary cutaneous neoplasms may be challenging and is often dependent on the identification of an adjacent conventional melanoma.

Matrical Tumors: A Comparative Molecular Analysis of Six Cases With Histological Correlations.

Pilomatrical tumors include pilomatricoma, melanocytic matricoma, and pilomatrical carcinoma. Similar to the normal anagen hair follicle bulb, they may be associated with benign and, rarely, with atypical pigmented dendritic melanocytes. It has been recently suggested that the term "melanocytic matricoma" be replaced with "pilomatricoma with melanocytic hyperplasia" (PMMH).

Exploring the genetic driver events of eccrine poromas and porocarcinomas: a retrospective, cross-institutional study of 54 cases.

We have comprehensively characterized the mutational landscape of eccrine poroma (EP) and eccrine porocarcinoma (EPC), uncovering novel molecular events and delineating different pathways of tumorigenesis underlying these tumours. EPs are driven largely by oncogenic fusion genes, whereas EPCs are driven largely by somatic mutations affecting various pathways, with a subset driven by fusion genes as the first oncogenic driver, and somatic mutations representing secondary events contributing to progression of the tumour. Fusion genes in EP predominantly involve , while those in EPC preferentially involve gene family members.

Exploration of the mutational landscape of cutaneous leiomyoma confirms FH as a driver gene and identifies targeting purine metabolism as a potential therapeutic strategy.

To comprehensively explore the mutational landscape of cutaneous leiomyoma (cLM) and identify candidate driver events, we performed a retrospective, multi-institutional, whole-exome sequencing and RNA sequencing study. We confirmed that a large proportion of patients with cLM have germline variants and additionally showed that somatic alteration of also drives cLM, with biallelic inactivation of being a frequent event. Treatment of -proficient and -deficient cell lines with the purine antagonist and chemotherapeutic agent, mercaptopurine, significantly decreased growth/colony formation; however, the addition of nucleosides was able to rescue only the -proficient cells, suggesting that purine metabolism is a targetable vulnerability for -deficient cLMs.

Role of Immunohistochemistry in the Diagnosis of Pilomatrical Tumors.

Pilomatrical skin tumors harbor mutations in CTNNB1 , which encodes for β-catenin, a downstream effector of the Wnt signaling pathway responsible for the differentiation, proliferation, and adhesion of epithelial stem cells. Therefore, downstream molecules, such as CDX2, LEF-1, and SATB2, in the Wnt signaling pathway could be useful diagnostic markers. Here, we sought to investigate the potential of immunohistochemistry (IHC) to differentiate between pilomatricoma and pilomatrical carcinoma, as well as from other cutaneous adnexal tumors.

ALK-rearranged, CD34-positive spindle cell neoplasms resembling dermatofibrosarcoma protuberans: a study of seven cases.

Aims: The majority of dermatofibrosarcoma protuberans (DFSP) harbour PDGFB or PDGFD rearrangements. We encountered ALK expression/rearrangement in a PDGFB/D-negative CD34-positive spindle cell neoplasm with features similar to DFSP, prompting evaluation of ALK-rearrangements in DFSP and plaque-like CD34-positive dermal fibroma (P-LDF).

Methods And Results: We searched the archives of academic institutions for cases previously coded as DFSP and P-LDF.

Cutaneous crystal storing histiocytosis: A case series with review of literature.

Crystal-storing histiocytosis (CSH) is a rare condition in which crystals accumulate in the cytoplasm of histiocytes and is usually associated with a lymphoplasmacytic neoplasm. Cutaneous CSH is extraordinarily rare and limited to case reports in the literature. We report two cases of this disease with cutaneous involvement.

MED15::ATF1-Rearranged Tumor: A Novel Cutaneous Tumor With Melanocytic Differentiation.

We recently described novel dermal tumors with melanocytic differentiation and morphologic and biological similarities to cutaneous clear cell sarcoma, including CRTC1::TRIM11 cutaneous tumor, and clear cell tumors with melanocytic differentiation and either ACTIN::MITF or MITF::CREM. Here, we describe a series of 3 patients presenting with tumors reminiscent of CRTC1::TRIM11 cutaneous tumor, found to demonstrate a novel MED15::ATF1 fusion. All 3 patients were children (5-16 years old).

Myxofibrosarcoma in adolescents and young adults: a clinicopathologic study of 17 cases.

Myxofibrosarcoma is a locally aggressive sarcoma that characteristically arises in the extremities of older patients. Cases arising at a younger age are rare, leading to diagnostic challenges. Our aim was to study the clinicopathologic features of myxofibrosarcoma in patients aged ≤40 years.

Subcutaneous Leiomyosarcoma: An Aggressive Malignancy Portending a Significant Risk of Metastasis and Death.

Subcutaneous leiomyosarcoma (LMS) is a rare, poorly understood variant. The current literature on the subject is sparse, consisting of isolated case reports and small clinicopathologic studies compromised by the inclusion of both its more common and indolent counterpart, cutaneous LMS (atypical intradermal smooth muscle neoplasm), as well as highly aggressive deep-seated tumors. Thus, precise clinicopathologic characterization is limited.