GLI1-Altered Mesenchymal Tumors With ACTB or PTCH1 Fusion: A Molecular and Clinicopathologic Analysis.

Mesenchymal tumors with GLI1 fusions or amplifications have recently emerged as a distinctive group of neoplasms. The terms GLI1-altered mesenchymal tumor or GLI1-altered soft tissue tumor serve as a nosological category, although the exact boundaries/criteria require further elucidation. We examined 16 tumors affecting predominantly adults (median age: 40 years), without sex predilection. Several patients had tumors of longstanding duration (>10 years). The most common primary site was soft tissue (n = 9); other sites included epidural tissue (n = 1), vertebra (n = 1), tongue (n = 1), hard palate (n = 1), and liver (n = 1). Histologically, the tumors demonstrated multinodular growth of cytologically uniform, ovoid-to-epithelioid, occasionally short spindled cells with delicate intratumoral vasculature and frequent myxoid stroma. Mitotic activity ranged from 0 to 8 mitoses/2 mm2 (mean 2). Lymphovascular invasion/protrusion of tumor cells into endothelial-lined vascular spaces was present or suspected in 6 cases. Necrosis, significant nuclear pleomorphism, or well-developed, fascicular spindle-cell growth were absent. Half demonstrated features of the newly proposed subset, "distinctive nested glomoid neoplasm." Tumors were consistently positive for CD56 (n = 5/5). A subset was stained with S100 protein (n = 7/13), SMA (n = 6/13), keratin (n = 2/9), EMA (n = 3/7), and CD99 (n = 2/6). Tumors harbored ACTB::GLI1 (n = 15) or PTCH1::GLI1 (n = 1) fusions. The assays used did not capture cases defined by GLI1 amplification. We also identified recurrent cytogenetic gains (1q, 5, 7, 8, 12, 12q13.2-ter, 21, and X). For patients with available clinical follow-up (n = 8), half were disease free. Half demonstrated distant metastases (lungs, bone, or soft tissue). Of cases without follow-up (n = 8), 2 were known recurrences, and 1 was presumed metastasis. Our results imply a more aggressive biological potential than currently reported. Given the possibility for metastasis and disease progression, even in cytologically bland, nested tumors, close clinical surveillance, akin to that for sarcoma management, may be indicated. The term GLI1-altered mesenchymal tumor with malignant potential is proposed.

Variable Genomic Landscapes of Advanced Melanomas with Heavy Pigmentation.

BACKGROUND: In the current study, we examined the real-world prevalence of highly pigmented advanced melanomas (HPMel) and the clinicopathologic, genomic, and ICPI biomarker signatures of this class of tumors. MATERIALS AND METHODS: Our case archive of clinical melanoma samples for which the ordering physician requested testing for both PD-L1 immunohistochemistry (IHC) and comprehensive genomic profiling (CGP) was screened for HPMel cases, as well as for non-pigmented or lightly pigmented advanced melanoma cases (LPMel). RESULTS: Of the 1268 consecutive melanoma biopsies in our archive that had been submitted for PD-L1 IHC, 13.0% (165/1268) were HPMel and 87.0% (1103/1268) were LPMel. In the HPMel cohort, we saw a significantly lower tumor mutational burden (TMB, median 8.8 mutations/Mb) than in the LPMel group (11.4 mut/Mb), although there was substantial overlap. In examining characteristic secondary genomic alterations (GA), we found that the frequencies of GA in TERTp, CDKN2A, TP53, and PTEN were significantly lower in the HPMel cases than in LPMel. A higher rate of GA in CTNNB1, APC, PRKAR1A, and KIT was identified in the HPMel cohort compared with LPMel. CONCLUSIONS: In this study, we quantified the failure rates of melanoma samples for PD-L1 testing due to high melanin pigmentation and showed that CGP can be used in these patients to identify biomarkers that can guide treatment decisions for HPMel patients. Using this practical clinical definition for tumor pigmentation, our results indicate that HPMel are frequent at 13% of melanoma samples, and in general appear molecularly less developed, with a lower TMB and less frequent secondary GA of melanoma progression.

Primary myxoid and epithelioid mesenchymal tumor of the kidney with a novel GLI1-FOXO4 fusion.

To our knowledge, we describe the first mesenchymal tumor with a novel GLI1-FOXO4 fusion gene. This well-circumscribed kidney tumor displayed variably myxoid and epithelioid histologic features with a focally nodular growth pattern. The tumor cells showed bland, round to ovoid nuclei, with no overt high-grade features. The tumor showed focal immunopositivity for smooth muscle actin and Melan-A, which raised the possibility of a relationship with a perivascular epithelioid cell tumor. The clinical and morphologic features appear distinct from other reported neoplasms harboring GLI1 or FOXO4 gene rearrangements. The patient underwent radical nephrectomy and is without evidence of disease during a relatively short clinical follow-up period. However, the features of this tumor likely warrant long-term follow-up to monitor for the possibility of a late recurrence or metastasis. In addition to reporting this novel fusion-positive tumor, we also provide a brief review of GLI1 and FOXO4 gene functions in both normal and neoplastic contexts.

CYLD mutation characterizes a subset of HPV-positive head and neck squamous cell carcinomas with distinctive genomics and frequent cylindroma-like histologic features.

Mutations in the tumor suppressor CYLD, known to be causative of cylindromas, were recently described in a subset of high-risk (hr) HPV-positive head and neck squamous cell carcinomas (HNSCC). Pathologic and genetic characterization of these CYLD-mutant carcinomas, however, remains limited. Here, we investigated whether CYLD mutations characterize a histopathologically and genomically distinct subset of hrHPV-positive HNSCC. Comprehensive genomic profiling via hybrid capture-based DNA sequencing was performed on 703 consecutive head and neck carcinomas with hrHPV sequences, identifying 148 unique cases (21%) harboring CYLD mutations. Clinical data, pathology reports, and histopathology were reviewed. CYLD mutations included homozygous deletions (n = 61/148; 41%), truncations (n = 52; 35%), missense (n = 26; 18%) and splice-site (n = 9; 6%) mutations, and in-frame deletion (n = 1; 1%). Among hrHPV-positive HNSCC, the CYLD-mutant cohort showed substantially lower tumor mutational burden than CYLD-wildtype cases (n = 555) (median 2.6 vs. 4.4 mut/Mb, p < 0.00001) and less frequent alterations in PIK3CA (11% vs. 34%, p < 0.0001), KMT2D (1% vs. 16%, p < 0.0001), and FBXW7 (3% vs. 11%, p = 0.0018). Male predominance (94% vs. 87%), median age (58 vs. 60 years), and detection of HPV16 (95% vs. 89%) were similar. On available histopathology, 70% of CYLD-mutant HNSCC (98/141 cases) contained hyalinized material, consistent with basement membrane inclusions, within crowded aggregates of tumor cells. Only 7% of CYLD-wildtype cases demonstrated this distinctive pattern (p < 0.0001). Histopathologic patterns of CYLD-mutant HNSCC lacking basement membrane inclusions included nonkeratinizing (n = 22, 16%), predominantly nonkeratinizing (nonkeratinizing SCC with focal maturation; n = 10, 7%), and keratinizing (n = 11, 8%) patterns. The latter two groups showed significantly higher frequency of PTEN alterations compared with other CYLD-mutant cases (38% [8/21] vs. 7% [8/120], p = 0.0004). Within our cohort of hrHPV-positive HNSCCs, CYLD mutations were frequent (21%) and demonstrated distinctive clinical, histopathologic, and genomic features that may inform future study of prognosis and treatment.

A pan-cancer analysis of PD-L1 immunohistochemistry and gene amplification, tumor mutation burden and microsatellite instability in 48,782 cases.

PD-L1 immunohistochemistry (IHC) currently has the most Food and Drug Administration (FDA) approvals as a companion diagnostic (CDx) for immunotherapies in specific tumor types; however, multiple other immunotherapy biomarkers exist. We performed this study to examine and report the prevalence of PD-L1 expression in a wide variety of tumor types and examine its relationship to microsatellite instability (MSI), tumor mutational burden (TMB), and CD274 (PD-L1) gene amplification. We performed a retrospective analysis of all cases in which both PD-L1 IHC (using the DAKO 22C3 IHC assay with either tumor proportion score (TPS) or combined positive score (CPS); or the VENTANA SP142 assay with infiltrating immune cell score (IC)) and comprehensive genomic profiling (CGP) were tested at Foundation Medicine between January 2016 and November 2019. Of note, PD-L1 positivity is defined per the CDx indication and tumor proportion score (TPS ≥ 1) for indications without a CDx claim; and TMB positivity is defined as ≥10 mutations/Mb. A total of 48,782 cases were tested for PD-L1 IHC and CGP. Immune cell expression of PD-L1 was more frequently identified than tumor cell expression of PD-L1. We saw a high correlation between PD-L1 expression and CD274 gene amplification (p < 0.0001), MSI and TMB (p < 0.0001), and PD-L1 and TMB (p < 0.0001). In addition, the combination of PD-L1 and TMB identified four unique disease subsets PD-L1-/TMB-, PD-L1+/TMB-, PD-L1-/TMB+, and PD-L1+/TMB+ with varying prevalence dependent on tumor type. Lastly, 50.3% (24527/48782) of the overall cohort was positive for at least one of the CDx or exploratory biomarkers described above. This is the largest pan-cancer analysis of relevant biomarkers associated with response to checkpoint inhibitors to date, including more than 48,000 cases. Additional clinical trials with treatment outcome data in individual tumor types are needed to determine whether the double positive PD-L1+/TMB+ disease subset would respond best to immunotherapy.

Melanoma with in-frame deletion of MAP2K1: a distinct molecular subtype of cutaneous melanoma mutually exclusive from BRAF, NRAS, and NF1 mutations.

While the genomics of BRAF, NRAS, and other key genes influencing MAP kinase (MAPK) activity have been thoroughly characterized in melanoma, mutations in MAP2K1 (MEK1) have received significantly less attention and have consisted almost entirely of missense mutations considered secondary oncogenic drivers of melanoma. Here, we investigated melanomas with in-frame deletions of MAP2K1, alterations characterized as MAPK-activating in recent experimental models. Our case archive of clinical melanoma samples with comprehensive genomic profiling by a hybrid capture-based DNA sequencing platform was searched for MAP2K1 genetic alterations. Clinical data, pathology reports, and histopathology were reviewed for each case. From a cohort of 7119 advanced melanomas, 37 unique cases (0.5%) featured small in-frame deletions in MAP2K1. These included E102_I103del (n = 11 cases), P105_A106del (n = 8), Q58_E62del (n = 6), I103_K104del (n = 5), I99_K104del (n = 3), L98_I103del (n = 3), and E41_F53del (n = 1). All 37 were wild type for BRAF, NRAS, and NF1 genomic alterations ("triple wild-type"), representing 2.0% of triple wild-type melanomas overall (37/1882). Median age was 66 years and 49% were male. The majority arose from primary cutaneous sites (35/37; 95%) and demonstrated a UV signature when available (21/25; 84%). Tumor mutational burden was typical for cutaneous melanoma (median = 9.6 mut/Mb, range 0-35.7), and frequently mutated genes included TERTp (63%), CDKN2A (46%), TP53 (11%), PTEN (8%), APC (8%), and CTNNB1 (5%). Histopathology revealed a spectrum of appearances typical of melanoma. For comparison, we evaluated 221 cases with pathogenic missense single nucleotide variants in MAP2K1. The vast majority of melanomas with missense SNVs in MAP2K1 showed co-mutations in BRAF (58%), NF1 (23%), or NRAS (18%). In-frame deletions in MAP2K1, previously shown in experimental models to be strongly MAPK-activating, characterized a significant subset of triple wild-type melanoma (2.0%), suggesting a primary oncogenic role for these mutations. Comprehensive genomic profiling of melanomas enables detection of this alteration, which may have implications for potential therapeutic options.

CYLD-mutant cylindroma-like basaloid carcinoma of the anus: a genetically and morphologically distinct class of HPV-related anal carcinoma.

Rare reports of anal carcinoma (AC) describe histologic resemblance to cutaneous cylindroma, but mutations in the tumor suppressor CYLD, the gene responsible for familial and sporadic cylindromas, have not been systematically investigated in AC. Here, we investigate CYLD-mutant AC, focusing on molecular correlates of distinct histopathology. Comprehensive genomic profiling (hybrid-capture-based DNA sequencing) was performed on 574 ACs, of which 75 unique cases (13%) harbored a CYLD mutation. Clinical data, pathology reports, and histopathology were reviewed for each CYLD-mutant case. The spectrum of CYLD mutations included truncating (n = 50; 67%), homozygous deletion (n = 10; 13%), missense (n = 16; 21%), and splice-site (n = 3; 4%) events. Compared with CYLD-wildtype AC (n = 499), CYLD-mutant ACs were significantly enriched for females (88% vs. 67%, p = 0.0001), slightly younger (median age 59 vs. 61 years, p = 0.047), and included near-universal detection of high-risk HPV sequences (97% vs. 88%, p = 0.014), predominantly HPV16 (96%). The CYLD-mutant cohort also showed significantly lower tumor mutational burden (TMB; median 2.6 vs. 5.2 mut/Mb, p < 0.00001) and less frequent alterations in PIK3CA (13% vs. 31%, p = 0.0015). On histopathologic examination, 73% of CYLD-mutant AC (55/75 cases) showed a striking cylindroma-like histomorphology, composed of aggregates of basaloid cells surrounded by thickened basement membranes and containing characteristic hyaline globules, while only 8% of CYLD-wildtype tumors (n = 34/409) contained cylindroma-like hyaline globules (p < 0.0001). CYLD-mutant carcinomas with cylindroma-like histomorphology (n = 55) showed significantly lower TMB compared with CYLD-mutant cases showing basaloid histology without the distinctive hyaline globules (n = 14) (median 1.7 vs. 4.4 mut/Mb, p = 0.0058). Only five CYLD-mutant cases (7%) showed nonbasaloid conventional squamous cell carcinoma histology (median TMB = 5.2 mut/Mb), and a single CYLD-mutant case showed transitional cell carcinoma-like histology. Within our cohort of ACs, CYLD mutations characterize a surprisingly large subset (13%), with distinct clinical and genomic features and, predominantly, a striking cylindroma-like histopathology, representing a genotype-phenotype correlation which may assist in classification of AC.

Melanomas with activating RAF1 fusions: clinical, histopathologic, and molecular profiles.

A subset of melanomas is characterized by fusions involving genes that encode kinases. Melanomas with RAF1 fusions have been rarely reported, mostly in clinical literature. To investigate this distinctive group of melanomas, we searched for melanomas with activating structural variants in RAF1, utilizing our case archive of clinical samples with comprehensive genomic profiling (CGP) by a hybrid capture-based DNA sequencing platform. Clinical data, pathology reports, and histopathology were reviewed for each case. RAF1 breakpoints, fusion partners, and co-occurring genetic alterations were characterized. From a cohort of 7119 melanomas, 40 cases (0.6%) featured fusions that created activating structural variants in RAF1. Cases with activating RAF1 fusions had median age of 62 years, were 58% male, and consisted of 9 primary tumors and 31 metastases. Thirty-nine cases were cutaneous primary, while one case was mucosal (anal) primary. Primary cutaneous melanomas showed variable architectures, including wedge-shaped and nodular growth patterns. Cytomorphology was predominantly epithelioid, with only one case, a desmoplastic melanoma, consisting predominantly of spindle cells. RAF1 5' rearrangement partners were predominantly intrachromosomal (n = 18), and recurrent partners included MAP4 (n = 3), CTNNA1 (n = 2), LRCH3 (n = 2), GOLGA4 (n = 2), CTDSPL (n = 2), and PRKAR2A (n = 2), all 5' of the region encoding the kinase domain. RAF1 breakpoints occurred in intron 7 (n = 32), intron 9 (n = 4), intron 5 (n = 2), and intron 6 (n = 2). Ninety-eight percent (n = 39) were wild type for BRAF, NRAS, and NF1 genomic alterations (triple wild type). Activating RAF1 fusions were present in 2.1% of triple wild-type melanomas overall (39/1882). In melanomas with activating RAF1 fusions, frequently mutated genes included TERTp (62%), CDKN2A (60%), TP53 (13%), ARID2 (10%), and PTEN (10%). Activating RAF1 fusions characterize a significant subset of triple wild-type melanoma (2.1%) with frequent accompanying mutations in TERTp and CDKN2A. CGP of melanomas may improve tumor classification and inform potential therapeutic options, such as consideration of specific kinase inhibitors.

Trichodysplasia spinulosa: Case reports and review of literature.

Trichodysplasia spinulosa (TS) is a rare skin condition caused by trichodysplasia spinulosa-associated polyomavirus (TSPyV). It affects immunosuppressed patients, and <50 cases have been reported. The majority of these cases are seen in solid organ transplant recipients. TS often poses a diagnostic and therapeutic challenge because of its rarity and resemblance with other skin conditions. Several forms of treatment are usually tried prior to establishing a definitive diagnosis. Oral valganciclovir and topical cidofovir have been found to give the best results and hence are the most commonly used agents once the diagnosis is established. Here, we present two cases with a review of literature of TS in solid organ transplant recipients, focusing on time to develop the condition post-transplant, immunosuppression regimen used, and treatment initiated both before and after a definitive diagnosis.

Utility of CD123 immunohistochemistry in differentiating lupus erythematosus from cutaneous T cell lymphoma.

AIMS: Histopathological overlap between lupus erythematosus and certain types of cutaneous T cell lymphoma (CTCL) is well documented. CD123+ plasmacytoid dendritic cells (PDCs) are typically increased in lupus erythematosus, but have not been well studied in CTCL. We aimed to compare CD123 immunostaining and histopathological features in these conditions. METHODS AND RESULTS: Skin biopsies of cutaneous lupus erythematosus (CLE, n = 18), lupus erythematosus panniculitis (LEP, n = 17), mycosis fungoides (MF, n = 25) and subcutaneous panniculitis-like T cell lymphoma (SPTCL, n = 9) were retrospectively reviewed and immunostained with CD123. Percentage, distribution and clustering of CD123+ cells were compared between CLE and MF and between LEP and SPTCL using χ2 and two-tailed t-tests. A higher percentage of CD123+ cells was observed in CLE than MF (P < 0.01), more frequently comprising ≥20% of the entire infiltrate (P < 0.01) and forming clusters (P < 0.01). Similarly, LEP showed a higher percentage of CD123+ cells than SPTCL (P = 0.01), more frequently comprising ≥20% of the infiltrate (P = 0.04) and forming clusters (P = 0.01). Basal vacuolar change or dyskeratosis was observed in all CLE cases and in 48% cases of MF cases (P = 0.05). Plasma cells were readily identified in 76% cases of LEP but in none of the SPTCL cases (P = 0.01). Adipocyte rimming by lymphocytes, hyaline fat necrosis and fibrinoid/grungy necrosis did not significantly differ between LEP and SPTCL. Dermal mucin also failed to distinguish between groups. CONCLUSIONS: CD123 immunostaining is helpful in differentiating CLE from MF and LEP from SPTCL, but should be interpreted in conjunction with clinicopathological features and other ancillary studies to ensure accurate diagnosis.

Cutaneous Metastasis of Gastroenteropancreatic Neuroendocrine Tumors (GEP-Nets).

BACKGROUND: Gastroenteropancreatic neuroendocrine tumors are neoplasms commonly found within the gastrointestinal tract that originate from endocrine cells. These are slow progressive tumors and often metastasize to other elements of the gastrointestinal tract including the liver. Consequently, these tumors release hormones including serotonin and/or histamine that are responsible for the symptoms including intermittent flushing and diarrhea. Metastasis of gastroenteropancreatic neuroendocrine tumors, although rare, is possible and may extend to local lymph nodes and viscera. CASE REPORT: Our patient was a 69-year-old female who initially presented with postprandial abdominal pain, nausea, vomiting, and later was diagnosed with gastroenteropancreatic neuroendocrine tumors following surgical resection in 2014. Restaging after surgery showed regional lymph node involvement and hepatic metastasis. Of note she did not have a pre-operative computed tomography scan. She was started on octreotide, and later switched to lanreotide. In the interim, she did not have any positive findings on serial octreoscans depicting the skin lesion that was performed in the interim period every six months. However, she noticed a cutaneous mass in the upper right flank mass in 2016, which was followed up by a dermatologist. In 2017, the mass grew in size and hence biopsied which showed neuroendocrine tumors consistent with her primary tumor. DISCUSSION: Gastroenteropancreatic neuroendocrine tumors often metastasize to lymph nodes and liver but rarely can involve the skin and present as firm papules as found in our patient. Cutaneous metastasis of gastroenteropancreatic neuroendocrine tumors often has high morbidity and mortality and is usually associated with a primary lesion in the bronchopulmonary system. However, as demonstrated in this case report, cutaneous metastasis can originate from the gastrointestinal tract, including the small intestine as well.

Melanoma arising in a nevus of Ito: novel genetic mutations and a review of the literature on cutaneous malignant transformation of dermal melanocytosis.

Dermal melanocytosis refers to a spectrum of benign melanocytic proliferations that includes Mongolian spot, nevus of Ota and nevus of Ito. These lesions most commonly occur in persons of Asian or African descent and are often present at birth or develop during childhood. Very rarely, dermal melanocytoses undergo malignant transformation. There have been only 13 reports in the literature of primary cutaneous melanoma arising in dermal melanocytoses. We report a case of a Chinese woman with melanoma arising in a congenital nevus of Ito. We performed targeted next-generation sequencing of the tumor which revealed mutations of GNAQ and BAP1, suggesting that alterations in these two genes led to malignant transformation of the nevus of Ito. We also provide a summary of reports in the literature regarding primary cutaneous melanoma arising in the context of dermal melanocytosis.

Histopathologic spectrum of hypersensitivity reactions associated with anti-CD52 therapy (alemtuzumab).

BACKGROUND: Alemtuzumab is a humanized monoclonal antibody directed against CD52, a cell surface antigen on B and T lymphocytes, and used to treat B-cell chronic lymphocytic leukemia and cutaneous T-cell lymphoma. Skin rash is a common adverse reaction following treatment with alemtuzumab. However, the clinicopathologic features and immunologic basis for the reaction have not been previously reported. METHODS: Our hospital's electronic pathology database was searched for cases with documentation of 'alemtuzumab' or 'anti-CD52' in the clinical history provided by either the ordering physician or the pathologist. Clinical and histopathologic review of the cases was performed. RESULTS: Five patients with cutaneous T-cell lymphoma (CTCL) or chronic lymphocytic leukemia (CLL) were treated with alemtuzumab, and developed pruritic, erythematous papules and plaques. Histopathology of the skin lesions revealed subacute spongiotic dermatitis with multifocal parakeratosis, endothelial activation and perivascular lymphocytic infiltrate. Eosinophils were not a prominent feature. CONCLUSIONS: We describe the clinicopathologic features of a novel hypersensitivity reaction to alemtuzumb, and hypothesize it may be due to an immunologic response precipitated by the persistence of resident memory T-cells (TRM ) in the skin. Our findings raise awareness for a novel reaction pattern and guide the histopathologic interpretation of lesions which may clinically mimic residual or recurrent cutaneous lymphoproliferative disorders.

Dermatopathologic manifestations of intravenous drug use.

BACKGROUND: The rate of intravenous drug use (IVDU) has been increasing nationally; however, cutaneous manifestations of IVDU have infrequently been investigated. We report a series of the clinicopathological correlation of IVDU in the skin. METHODS: A search of surgical pathology files between the years 2000 and 2014 was performed for cutaneous specimens from patients with a reported history of IVDU for which the histopathological findings could not be attributed to another etiology. Ten cases for which slides were available were included in the study. RESULTS: Patients had an average age of 39.7 years and had active or recent history of IVDU. Clinical impressions included ulcer, granulomatous dermatitis, vasculitis, pyoderma gangrenosum and hyperpigmentation at injection sites. Histopathology revealed leukocytoclastic vasculitis (n = 2), dermal pigment deposition (n = 3), non-specific ulceration/scarring (n = 4) and necrobiosis lipoidica-like dermatitis (n = 1). No infectious etiology or polarizable foreign material was identified in any case. CONCLUSIONS: Cutaneous manifestations of IVDU should be considered in the differential as an etiology for dermatopathologic findings in high-risk patients. We report histopathological findings beyond the scope of those most commonly associated with IVDU. We aim to raise awareness of the cutaneous manifestations of IVDU to improve clinicopathological correlation and patient management in light of the ongoing epidemic.

Peutz-Jeghers syndrome: a critical look at colonic Peutz-Jeghers polyps.

Peutz-Jeghers syndrome is an autosomal dominant condition characterized by gastrointestinal hamartomatous polyps. The pathologic identification of a Peutz-Jeghers polyp is integral to the diagnosis of this syndrome that often remains undiagnosed until after these polyps are identified. Histologically, Peutz-Jeghers polyps are characterized by a distinctive arborization of smooth muscle within the lamina propria. Colonic Peutz-Jeghers polyps, however, may mimic mucosal prolapse polyps or virtually any colonic polyp that undergoes prolapse. In this paper, we explore the morphological features of colonic Peutz-Jeghers polyps and the diagnostic challenges associated with these polyps. Colonic polyps from patients with Peutz-Jeghers syndrome were identified (n=34). The control cohort, included mucosal prolapse polyps (n=5), hyperplastic polyps (n=10) and tubular adenomas with prolapse (n=9), ganglioneuromatous polyps (n=2) and juvenile polyps (n=14). Intramucosal smooth muscle fibers were identified in all classes of polyps. Twenty-three of the 34 colonic Peutz-Jeghers polyps were characterized by lobulated clusters of colonic crypts. On immunohistochemistry, desmin-positive smooth muscle fibers were seen surrounding these lobules. This lobular organization of the crypts was not identified in mucosal prolapse polyps and hyperplastic polyps or tubular adenomas with prolapse; only one of the 14 juvenile polyps showed this pattern of reactivity on a desmin stain. Our data suggests that the histologic hallmark of colonic Peutz-Jeghers polyps is the lobular organization of the crypts, and that an arborizing pattern of smooth muscle proliferation is neither sensitive nor a specific marker of colonic Peutz-Jeghers polyps. The presence of desmin-positive smooth muscle fibers surrounding the lobules is a helpful diagnostic feature of colonic Peutz-Jeghers polyps, and facilitates the distinction of these polyps from non-Peutz-Jeghers polyps with prolapse-like changes.

Microcystic adnexal carcinoma versus desmoplastic trichoepithelioma: a comparative study.

The histologic distinction between microcystic adnexal carcinoma (MAC) and desmoplastic trichoepithelioma (dTE) can be challenging in the setting of a superficial biopsy. However, accurate diagnosis has treatment implication because the standard of care for MAC is wide local excision but more conservative care for dTE. We reviewed the histologic features of 30 MAC and 39 dTE cases and performed cytokeratin (CK) 17, CK19, and epidermal growth factor receptor (EGFR) immunostains on 20 MACs and 18 dTEs. MAC cases occurred in older patients in comparison with dTE (median, 67 years vs. 34 years). The head and neck was the most commonly involved site, 88% and 89% for MAC and dTE, respectively. In addition to features previously reported as specific for MAC, such as skeletal muscle and subcutaneous tissue invasion, perineural invasion, and ductal differentiation, we found the presence of mitotic figures to be significantly more frequent in MAC cases (P < 0.0001). In contrast, the presence of keratocyst, keratin granuloma, and calcification was significantly more frequent in dTE cases (P < 0.0001). CK19 seems to be a helpful adjunct because its expression was seen in 70% (14/20) of MAC versus 22% (4/18) of dTE cases (P = 0.0044); however, the clinical usefulness in individual cases may be limited because of the overlapping immunoprofile. CK17 and EGFR expression was seen in all the MAC and dTE cases. Low polysomy of EGFR gene was observed in only one MAC case, suggesting that molecular mechanisms other than gene amplification play a role in EGFR overexpression.

Basal cell carcinoma with osteosarcomatous component.

Sarcomatoid carcinoma or carcinosarcomas of the skin are rare. Basal cell carcinoma (BCC) with osteosarcomatous differentiation is the second most common sarcomatoid carcinoma of the skin, following squamous cell carcinoma with heterologous mesenchymal differentiation. There are only 11 cases of BCC with osteosarcomatous component reported in the literature, with limited documented molecular analyses. The authors report the clinical and histological features of 2 cases with molecular analyses for recurrent mutations in 17 cancer genes. In both cases, the epithelial or BCC component was positive for BerEP4 and high-molecular weight cytokeratin, whereas the sarcomatous component was negative for both markers. Mutational analyses revealed TP53 mutation in 1 case with p53 expression noted in both components. The other case was negative for both p53 expression and TP53 mutation.

Expanding Our Knowledge of Molecular Pathogenesis in Histiocytoses: Solitary Soft Tissue Histiocytomas in Children With a Novel CLTC::SYK Fusion.

The histiocytoses comprise a histopathologically and clinically diverse group of disorders bearing recurrent genomic alterations, commonly involving the BRAF gene and mitogen-activated protein kinase pathway. In the current study, a novel CLTC :: SYK fusion in 3 cases of a histopathologically distinct histiocytic neoplasm arising as solitary soft tissue lesions in children identified by next-generation sequencing and fluorescence in situ hybridization is described. Morphologically, all 3 neoplasms were composed of sheets of cells with round-oval nuclei and vacuolated eosinophilic cytoplasm but, in contrast to classic juvenile xanthogranuloma (JXG), Touton giant cells were absent. A separate cohort of classic JXG cases subsequently profiled by fluorescence in situ hybridization were negative for the presence of a CLTC::SYK fusion suggesting that CLTC::SYK fusion-positive histiocytoma is genetically and histologically distinct from JXG. We postulate that the CLTC::SYK fusion leads to aberrant activation of the SYK kinase, which is involved in variable pathways, including mitogen-activated protein kinase. The identification of a novel CLTC::SYK fusion may pave the way for the development of targeted therapeutic options for aggressive disease.