Epidermal nevi and epidermolytic hyperkeratosis: A review of cases, highlighting indications for biopsy and genetics referral.

Epidermal nevi are common benign cutaneous hamartomas that may rarely demonstrate histopathologic evidence of epidermolytic hyperkeratosis (EHK), representing cutaneous mosaicism for pathogenic keratin variants. Rarely, individuals with linear epidermal nevi transmit to their children the inherited form of EHK, also known as epidermolytic ichthyosis, characterized by generalized erythema, blistering, and scaling at birth evolving to widespread hyperkeratosis. We present an updated review of reported cases of linear epidermal nevi with EHK exhibiting transmission of epidermolytic ichthyosis to guide important considerations in the care of individuals with epidermal nevi. Clinical characteristics of linear epidermal nevi do not reliably predict the presence of EHK. All reported cases of transmission to offspring have occurred in individuals with linear epidermal nevi involving more than one anatomic area suggesting increased reproductive risk with involvement of two or more anatomic sites. Therefore, genetics consultation is recommended for these individuals with biopsy-confirmed EHK. For individuals with smaller areas of epidermal nevus involvement, the implications are less well known, though genetics consultation may still be considered for those interested in further discussion of general reproductive risk.

Proliferating inverted follicular keratosis of genital skin: Case series of a challenging variant.

BACKGROUND: Inverted follicular keratosis (IFK) is a benign cutaneous epithelial tumor typically presenting as a small papule on the head and neck. We have encountered deep endophytic tumors on genital skin with some characteristics of IFK but also atypical features, raising concern for squamous cell carcinoma (SCC). METHODS: Four such tumors were identified in our database. Histopathologic analysis and ancillary studies were performed. RESULTS: All patients were young women who presented with a solitary 0.5-1.0 cm lesion on the vulva, perineum, or inner buttock. Each showed a squamous proliferation arising from the epidermis, with endophytic growth that was deep and bulbous but not infiltrative. The tumor lobules contained eosinophilic keratinocytes, forming numerous squamous eddies. Small irregular spaces and dyskeratotic cells were frequently found. Nuclear pleomorphism was minimal to absent. All demonstrated wild-type p53 expression and lack of p16 block positivity. In situ hybridizations for human papillomavirus were negative. None of the three cases with follow-up data showed evidence of recurrence. CONCLUSIONS: The absence of infiltrative growth or significant pleomorphism, the presence of numerous squamous eddies, the reassuring immunoprofile, and the lack of evidence of recurrence support a variant of IFK and speak against SCC. We propose the term "proliferating IFK" to highlight the florid squamous proliferation. Recognition of this unusual variant would avoid overdiagnosis of SCC.

Nonspecificity of Immunohistochemistry for Mycobacteria Species Using a Rabbit Polyclonal Antibody.

CONTEXT.­: Recent publications have featured immunohistochemistry (IHC) as a sensitive tool for detecting Mycobacterium tuberculosis and nontuberculous mycobacteria, but performance is limited to cases suspected to have mycobacterial infection. OBJECTIVE.­: To examine cross-reactivity of a polyclonal antimycobacterial antibody with various types of pathogens, tissues, and inflammatory patterns. DESIGN.­: Surgical pathology files during a period of 6 years were searched, and 40 cases representing a variety of pathogens, tissue types, and inflammatory responses were retrieved. Cases were stained with a rabbit polyclonal antimycobacterial antibody (Biocare Medical, Pacheco, California). The cases and associated histochemical stains, culture, and molecular results were reviewed by 3 pathologists. RESULTS.­: All 8 cases of mycobacterial infection previously diagnosed by other methods were positive for mycobacteria by IHC. In addition, multiple bacterial and fungal organisms and 1 case of Leishmania amastigotes were also immunoreactive with the mycobacterial IHC. CONCLUSIONS.­: Although highly sensitive for mycobacteria, the polyclonal antibody shows significant cross-reactivity with other organisms. This is a sensitive but nonspecific stain that can be used as an alternative confirmation method for mycobacteria, but attention should be paid to inflammatory reaction and organism morphology when IHC is positive to avoid misdiagnosis.

Evaluation of TRIM63 RNA in situ hybridization (RNA-ISH) as a potential biomarker for alveolar soft-part sarcoma (ASPS).

Alveolar soft-part sarcoma (ASPS) is a rare soft tissue tumor with a broad morphologic differential diagnosis. While histology and immunohistochemistry can be suggestive, diagnosis often requires exclusion of other entities followed by confirmatory molecular analysis for its characteristic ASPSCR1-TFE3 fusion. Current stain-based biomarkers (such as immunohistochemistry for cathepsin K and TFE3) show relatively high sensitivity but may lack specificity, often showing staining in multiple other entities under diagnostic consideration. Given the discovery of RNA in situ hybridization (RNA-ISH) for TRIM63 as a sensitive and specific marker of MiTF-family aberration renal cell carcinomas, we sought to evaluate its utility in the workup of ASPS. TRIM63 RNA-ISH demonstrated high levels (H-score greater than 200) of expression in 19/20 (95%) cases of ASPS (average H-score 330) and was weak or negative in cases of paraganglioma, clear cell sarcoma, rhabdomyosarcoma, malignant epithelioid hemangioendothelioma, as well as hepatocellular and adrenal cortical carcinomas. Staining was also identified in tumors with known subsets characterized by TFE3 alterations such as perivascular epithelioid cell neoplasm (PEComa, average H-score 228), while tumors known to exhibit overexpression of TFE3 protein without cytogenetic alterations, such as melanoma and granular cell tumor, generally showed less TRIM63 ISH staining (average H-scores 147 and 96, respectively). Quantitative assessment of TRIM63 staining by RNA-ISH is potentially a helpful biomarker for tumors with molecular TFE3 alterations such as ASPS.

Molecular Profiling of Syringocystadenocarcinoma Papilliferum Reveals RAS-Activating Mutations.

CONTEXT.­: Syringocystadenocarcinoma papilliferum (SCACP) is a rare adnexal carcinoma and the malignant counterpart of syringocystadenoma papilliferum (SCAP), which is commonly located on the head and neck and may arise in association with a nevus sebaceus. RAS mutations have been identified in both SCAP and nevus sebaceus. OBJECTIVE.­: To evaluate the clinicopathologic and molecular features of SCACPs, which have not been previously explored. DESIGN.­: We obtained 11 SCACPs from 6 institutions and reviewed the clinicopathologic features. We also performed molecular profiling using next-generation sequencing. RESULTS.­: The cohort comprised 6 women and 5 men with ages ranging from 29 to 96 years (mean, 73.6 years). The neoplasms occurred on the head and neck (n = 8; 73%) and extremities (n = 3; 27%). Three tumors possibly arose in a nevus sebaceus. A total of 4 cases showed at least carcinoma in situ (adenocarcinoma, n = 3; squamous cell carcinoma [SCC], n = 1), and 7 cases were invasive (SCC, n = 5; mixed adenocarcinoma + SCC, n = 2). A total of 8 of 11 cases (73%) had hot spot mutations consisting of HRAS (n = 4), KRAS (n = 1), BRAF (n = 1), TP53 (n = 4), ATM (n = 2), FLT3 (n = 1), CDKN2A (n = 1), and PTEN (n = 1). All 4 cases with HRAS mutations occurred on the head and neck, whereas the KRAS mutation occurred on the extremity. CONCLUSIONS.­: RAS-activating mutations were detected in 50% of the cases, of which most (80%) involved HRAS and occurred on the head and neck, which shows overlapping features with SCAP, supporting that a subset may arise as a result of malignant transformation and likely an early oncogenic event.

Characterization of T-Helper Immune Phenotype in Symmetrical Drug-Related Intertriginous and Flexural Exanthema (SDRIFE) Endorses a Delayed-Type Hypersensitivity Reaction.

ABSTRACT: Symmetrical drug-related intertriginous and flexural exanthema (SDRIFE) is a cutaneous drug eruption with a characteristic distribution of erythema on the gluteal/inguinal region and intertriginous areas with unclear pathogenesis. In this study, we aimed to characterize the T-helper immune phenotype in SDRIFE in comparison with psoriasis and eczema to further the understanding of the pathophysiology and immune response of this rare disorder. Immunohistochemical staining was performed on 9 skin biopsies each from SDRIFE, psoriasis, and eczema using immunohistochemistry for CD3 and dual CD4/T-bet, CD4/GATA3, and CD4/RORC to quantify the percentage of Th1, Th2, and Th17 cells, respectively. A significant difference was detected in the average percentage of Th1 between all 3 groups with the highest percentage of Th1 cells seen in psoriasis, followed by SDRIFE and eczema. SDRIFE showed significantly lower Th2 expression as compared to both psoriasis and eczema. There was a trend towards a higher average percentage of Th17 in psoriasis and SDRIFE, and the ratio of Th17:Th2 was significantly higher in samples of SDRIFE compared with both eczema and psoriasis. The findings characterize SDRIFE as a Th1 and possibly Th17-driven process, which could inform future therapeutic options and substantiate the model of SDRIFE as a delayed-type hypersensitivity reaction.

Clinical and Histopathologic Spectrum of Toxic Erythema of Chemotherapy: A Series of 56 Cases From a Single Institution.

INTRODUCTION: Although many individual cases and small series of toxic erythema of chemotherapy (TEC) have been described, the full spectrum of findings is not well understood. OBJECTIVE: To provide a comprehensive review of the clinical and histopathologic features of TEC with an emphasis on novel histopathologic findings. METHODS: We searched our electronic medical record for "toxic erythema of chemotherapy" or "neutrophilic eccrine hidradenitis." Fifty-six cases meeting clinical and histopathologic criteria were identified. The electronic medical record and accompanying hematoxylin and eosin-stained slides were retrospectively reviewed. RESULTS: The clinical findings were heterogeneous but included classic presentations such as intertriginous eruptions (34%) and acral erythema (25%). The most common histopathologic features were apoptotic keratinocytes (95%), basal vacuolar change (91%), and epithelial dysmaturation (79%). Eccrine squamous syringometaplasia was seen in over half of the cases (33/56; 59%), whereas neutrophilic eccrine hidradenitis was uncommon (16%). Interestingly, many cases showed prominent interstitial histiocytes (55%). Other novel findings included irregular orthohyperkeratosis (23%), irregular epidermal hyperplasia (14%), and acantholysis (9%). LIMITATIONS: As a retrospective study, it is subject to information bias. CONCLUSION: This is the largest reported series of TEC. In addition to confirming previously reported features, we identify novel histopathologic findings to add to the spectrum of TEC.

Margin status in vulvovaginal melanoma: Management and oncologic outcomes of 50 cases.

Objectives: To determine the influence of margin status, including preinvasive disease at the margin, on local recurrence and overall survival (OS) in patients with vulvovaginal melanoma. Methods: All patients with Stage 0-III vulvovaginal melanoma treated with primary surgical management between 1/2010-12/2019 were included. Margin status was categorized as negative, preinvasive disease (atypical junctional melanocytic hyperplasia and melanoma in situ), and invasive melanoma. Kaplan-Meier analyses were performed for local progression free survival (PFS) and OS. The impact of clinical and pathologic factors on local PFS and OS were assessed with Cox-regression analyses. Results: Fifty patients with a median follow-up of 48 months (range 3-119) were included. The median age was 63 years (range 20-83). Twenty percent (N = 10) had Stage 0 disease, 18% (N = 9) had Stage I, 46% (N = 23) had Stage II, and 16% (N = 8) had Stage III. Forty-four percent (N = 22) of patients had negative surgical margins, 46% (N = 23) had preinvasive disease at the margins, and 10% (N = 5) had invasive melanoma at the margins. The 5-year local PFS was 63% (95% CI: 42-78%) and OS was 60% (95% CI: 42-74%). Age, Breslow depth, stage, margin status, and re-resection did not significantly impact local PFS. In patients with preinvasive disease at the margin, all who recurred locally had Stage I-II disease. Conclusion: Preinvasive disease at the surgical margins may play an important role in local recurrence in patients with Stage I-II vulvovaginal melanoma. Patients with early (Stage 0) and advanced (Stage III) disease rarely recur locally and may not benefit from re-resection.

CD30 expression in cutaneous B-cell lymphomas.

INTRODUCTION: CD30 expression has been infrequently described in cutaneous B-cell lymphomas (CBCLs). We examined CD30 expression in reactive lymphoid hyperplasia (RLH) and CBCL and correlated expression with clinicopathologic features. METHODS: CD30 was examined in 82 CBCL patients and 10 RLH patients that had been evaluated in our cutaneous lymphoma clinics. The CBCL patients included: primary cutaneous follicle center lymphoma (PCFCL), Grade 1/2 systemic/nodal follicular lymphoma (SFL); primary cutaneous marginal zone lymphoma/lymphoproliferative disorder (PCMZL/LPD); systemic marginal zone lymphoma (SMZL); primary cutaneous diffuse large B-cell lymphoma, leg type (PCDLBCL-LT); and extracutaneous/systemic diffuse large B-cell lymphoma (eDLBCL). We scored CD30 expression for intensity and extent and related CD30 expression to age at first diagnosis, sex, site of biopsy, clinical appearance, extracutaneous involvement, multiple cutaneous lesions, B-symptoms, lymphadenopathy, positive positron emission tomography/computed tomography (PET/CT), elevated lactate dehydrogenase (LDH), and positive bone marrow biopsy. RESULTS: CD30 expression was identified in 35% of CBCL, ranging from few, weak, scattered cells to strong and diffuse expression. It was most common in PCFCL and was not expressed in PCDLBCL-LT. Rare PCFCL expressed strong, diffuse CD30. Some cases of PCMZL/LPD, SMZL, FL, and RLH showed scattered, strongly positive cells. CD30 expression in CBCL was associated with favorable clinical features: younger age, negative PET/CT, and an LDH within normal limits. CONCLUSIONS: CD30 may be expressed in CBCL, possibly causing diagnostic confusion. CD30 expression was most commonly identified in PCFCL and is associated with favorable clinical features. In cases with strong and diffuse expression, CD30 could be a therapeutic target.

Utility of GLI1 RNA Chromogenic in Situ Hybridization in Distinguishing Basal Cell Carcinoma From Histopathologic Mimics.

Basal cell carcinoma (BCC) is the most common human malignancy and is a leading cause of nonmelanoma skin cancer-related morbidity. BCC has several histologic mimics which may have treatment and prognostic implications. Furthermore, BCC may show alternative differentiation toward a variety of cutaneous structures. The vast majority of BCCs harbor mutations in the hedgehog signaling pathway, resulting in increased expression of the GLI family of transcription factors. GLI1 immunohistochemistry has been shown to discriminate between several tumor types but demonstrates high background signal and lack of specificity. In this study, we evaluated the utility of GLI1 RNA chromogenic in situ hybridization (CISH) as a novel method of distinguishing between BCC and other epithelial neoplasms. Expression of GLI1 by RNA CISH was retrospectively evaluated in a total of 220 cases, including 60 BCCs, 37 squamous cell carcinomas (SCCs) including conventional, basaloid, and human papillomavirus infection (HPV)-associated tumors, 16 sebaceous neoplasms, 10 Merkel cell carcinomas, 58 benign follicular tumors, and 39 ductal tumors. The threshold for positivity was determined to be greater than or equal to 3 GLI1 signals in at least 50% of tumor cells. Positive GLI1 expression was identified in 57/60 BCCs, including metastatic BCC, collision lesions with SCC, and BCCs with squamous, ductal, or clear cell differentiation or with other unusual features compared to 1/37 SCCs, 0/11 sebaceous carcinomas, 0/5 sebaceomas, 1/10 Merkel cell carcinomas, 0/39 ductal tumors, and 28/58 follicular tumors. With careful evaluation, GLI1 RNA CISH is highly sensitive (95%) and specific (98%) in distinguishing between BCC and nonfollicular epithelial neoplasms. However, GLI1 CISH is not specific for distinguishing BCC from most benign follicular tumors. Overall, detection of GLI1 RNA by CISH may be a useful tool for precise classification of histologically challenging basaloid tumors, particularly in the setting of small biopsy specimens, metaplastic differentiation, or metastatic disease.

Multiplex Immunohistochemistry and Immunofluorescence: A Practical Update for Pathologists.

Our understanding of the biology and management of human disease has undergone a remarkable evolution in recent decades. Improved understanding of the roles of complex immune populations in the tumor microenvironment has advanced our knowledge of antitumor immunity, and immunotherapy has radically improved outcomes for many advanced cancers. Digital pathology has unlocked new possibilities for the assessment and discovery of the tumor microenvironment, such as quantitative and spatial image analysis. Despite these advances, tissue-based evaluations for diagnosis and prognosis continue to rely on traditional practices, such as hematoxylin and eosin staining, supplemented by the assessment of single biomarkers largely using chromogenic immunohistochemistry (IHC). Such approaches are poorly suited to complex quantitative analyses and the simultaneous evaluation of multiple biomarkers. Thus, multiplex staining techniques have significant potential to improve diagnostic practice and immuno-oncology research. The different approaches to achieve multiplexed IHC and immunofluorescence are described in this study. Alternatives to multiplex immunofluorescence/IHC include epitope-based tissue mass spectrometry and digital spatial profiling (DSP), which require specialized platforms not available to most clinical laboratories. Virtual multiplexing, which involves digitally coregistering singleplex IHC stains performed on serial sections, is another alternative to multiplex staining. Regardless of the approach, analysis of multiplexed stains sequentially or simultaneously will benefit from standardized protocols and digital pathology workflows. Although this is a complex and rapidly advancing field, multiplex staining is now technically feasible for most clinical laboratories and may soon be leveraged for routine diagnostic use. This review provides an update on the current state of the art for tissue multiplexing, including the capabilities and limitations of different techniques, with an emphasis on potential relevance to clinical diagnostic practice.

Detection of antibody-coated Mucor in skin biopsy by direct immunofluorescence.

Cutaneous mucormycosis may be caused by direct inoculation or hematogenous spread of mucormycetes in immunocompromised patients. Skin biopsy is characterized by a deep fungal infection with frequent angioinvasion. The fungal hyphae can usually be identified on H&E stain. We report a case of cutaneous angioinvasive mucormycosis in which the fungi were also visualized on direct immunofluorescence. A 57-year-old patient with relapsed myelodysplastic syndrome status-post allogeneic hematopoietic cell transplant, diabetes mellitus, and graft-versus-host disease presented with painful, palpable, dark-red to violaceous retiform purpuric plaques. Light microscopy of punch biopsy revealed numerous broad, ribbon-like, pauci-septate hyphae in the dermis with angioinvasion, consistent with mucormycosis. Direct immunofluorescence performed on a concurrent biopsy to exclude immune complex vasculitis showed smooth IgG, IgA (weak), IgM (faint), and C3 deposition on the hyphal structures, compatible with antibody-coated fungi. Tissue culture subsequently confirmed Mucor species. Although mucormycosis was readily diagnosable on routine light microscopy in this case, recognition of the unique phenomenon of antibody-coated fungi can be crucial when the invasive fungi are sparse or only present in the direct immunofluorescence specimen.

Expression of SATB2 in primary cutaneous sarcomatoid neoplasms: a potential diagnostic pitfall.

SATB2 can be used as an immunohistochemical marker for osteoblastic differentiation. The differential diagnosis of a cutaneous sarcomatoid neoplasm sometimes includes osteosarcoma when the tumour concomitantly involves the skin, soft tissue, and bone, or when there is a past medical history of osteosarcoma. As the utility of SATB2 immunohistochemistry in these scenarios was unclear, we aimed to determine the frequency and the pattern of SATB2 expression in a variety of cutaneous sarcomatoid neoplasms. SATB2 expression by immunohistochemistry was evaluated by intensity (0-3) and extent (0-100%) of staining to generate an h-score for each case. Expression levels were classified into high-positive (h-score ≥100), low-positive (20-99), and negative (<20) groups. Positive SATB2 expression was observed in 18/23 (78%) atypical fibroxanthomas (AFX), 10/19 (53%) pleomorphic dermal sarcomas, 9/20 (45%) cutaneous sarcomatoid squamous cell carcinomas, 14/39 (36%) sarcomatoid melanomas, 2/13 (15%) poorly differentiated cutaneous angiosarcomas, 10/17 (59%) high-grade cutaneous leiomyosarcomas, and 7/8 (88%) osteosarcoma controls. With the exception of AFX, all cutaneous neoplasms showed significantly lower average h-scores than osteosarcoma. AFX gave the highest average h-score (71) and percentage of high-positive cases (48%) among all examined cutaneous neoplasms. Only two (1.5%) of all cutaneous cases showed strong intensity of staining. Common SATB2 expression in various cutaneous sarcomatoid neoplasms poses a potential diagnostic pitfall when the differential diagnosis includes osteosarcoma. Requirement of strong staining and a high-positive h-score improves the specificity of SATB2 in differentiating these tumours from osteosarcoma.

Interobserver Agreement Across Subspecialties for Diagnosis of Differentiated Vulvar Intraepithelial Neoplasia and Predictive Values of 20 Histologic Features.

CONTEXT.­: Differentiated vulvar intraepithelial neoplasia (dVIN) is a human papillomavirus-independent lesion with the potential for rapid progression to invasive squamous cell carcinoma (SCC). The histopathologic features of dVIN are diverse, have overlapping characteristics with lichen sclerosus (LS) and lichen simplex chronicus (LSC), and may be diagnosed by dermatopathologists or gynecologic pathologists because of the vulva's anatomic location. OBJECTIVES.­: To identify the salient histopathologic features of dVIN, particularly those that predict progression to SCC, and to evaluate interobserver agreement in diagnosing dVIN within the same subspecialty and across subspecialties. DESIGN.­: One general surgical pathologist, 2 pathology-trained dermatopathologists, and 1 gynecologic pathologist blinded to the final diagnoses were asked to record 20 histopathologic features and to provide their final interpretations on cases of dVIN (n = 65), LS (n = 126), LSC (n = 112), and LS with LSC (n = 6). RESULTS.­: Interobserver agreement for the 4 diagnoses and 10 histopathologic features was moderate. Logistic regression analysis indicated that keratin pearls, basal pleomorphism, and basal layer disarray were independent variables for diagnosing dVIN (coefficients 1.95, 1.97, and 0.91, respectively; P < .001) and progression to SCC (coefficients 1.96, 1.20, and 1.08, respectively; P < .001). CONCLUSIONS.­: There is no single histopathologic feature pathognomonic for dVIN; however, the presence of keratin pearls, basal pleomorphism, and basal layer disarray should raise high suspicion for dVIN and concurrent SCC. Expertise in both dermatologic and gynecologic pathology is beneficial for diagnosing dVIN.

Analysis of residual disease in periocular basal cell carcinoma following hedgehog pathway inhibition: Follow up to the VISORB trial.

Basal cell carcinoma (BCC) is a common skin cancer caused by deregulated hedgehog signaling. BCC is often curable surgically; however, for orbital and periocular BCCs (opBCC), surgical excision may put visual function at risk. Our recent clinical trial highlighted the utility of vismodegib for preserving visual organs in opBCC patients: 67% of patients displayed a complete response histologically. However, further analysis of excision samples uncovered keratin positive, hedgehog active (Gli1 positive), proliferative micro-tumors. Sequencing of pre-treatment tumors revealed resistance conferring mutations present at low frequency. In addition, one patient with a low-frequency SMO W535L mutation recurred two years post study despite no clinical evidence of residual disease. Sequencing of this recurrent tumor revealed an enrichment for the SMO W535L mutation, revealing that vismodegib treatment enriched for resistant cells undetectable by traditional histology. In the age of targeted therapies, linking molecular genetic analysis to prospective clinical trials may be necessary to provide mechanistic understanding of clinical outcomes. Trial Registration: ClinicalTrials.gov Identifier: NCT02436408.

PRAME expression in spindle cell melanoma, malignant peripheral nerve sheath tumour, and other cutaneous sarcomatoid neoplasms: a comparative analysis.

Diagnosis of spindle cell/sarcomatoid melanoma may be challenging due to frequent loss of expression of melanocytic marker(s) and histomorphologic resemblance to various mesenchymal tumours, particularly malignant peripheral nerve sheath tumour (MPNST). Overexpression of PReferentially expressed Antigen in MElanoma (PRAME) supports a diagnosis of melanoma when evaluating challenging melanocytic tumours. PRAME expression in MPNST and other cutaneous sarcomatoid neoplasms, however, has not been well characterised. We aimed to determine the utility of PRAME immunostain in distinguishing spindle cell melanoma from MPNST and other sarcomatoid mimics. PRAME expression was scored by extent (0 to 4+) and intensity (0 to 3) of staining. A strong positive correlation was observed between the extent and intensity scores (r = 0.84). An extent score of 4+, defined by staining in 76-100% of tumour cells, was seen in 56% (23/41) of spindle cell melanomas, 18% (7/38) of MPNSTs, 15% (4/27) of cutaneous sarcomatoid squamous cell carcinomas (SCCs), 33% (5/15) of poorly differentiated cutaneous angiosarcomas, 12% (4/33) of atypical fibroxanthomas (AFXs), 4% (1/25) of pleomorphic dermal sarcomas (PDSs), and none (0/16) of the high-grade cutaneous leiomyosarcomas. A significant difference was found between spindle cell melanoma and all other examined sarcomatoid neoplasms except angiosarcoma. While diffuse (and often strong) PRAME expression is more frequently observed in spindle cell melanoma than MPNST, sarcomatoid SCC, AFX, PDS, and high-grade leiomyosarcoma, its limited sensitivity and specificity caution against its use as a standalone diagnostic marker. PRAME may complement other epigenetic or lineage-specific markers and should only be used as part of an immunohistochemical panel when evaluating these sarcomatoid neoplasms.

Microsecretory Adenocarcinoma of the Ear Canal: Novel Cutaneous Analog of a Salivary Gland Neoplasm.

ABSTRACT: Microsecretory adenocarcinoma (MSA) of the salivary gland is a new entity recently added to the World Health Organization Classification of Head and Neck Tumors. This tumor is characterized by a recurrent MEF2C-SS18 translocation. We present a nodular tumor confined to the dermis of the ear canal of a 44-year-old patient, which demonstrated classic histopathologic features and molecular alteration of MSA. Specifically, the tumor was composed of numerous tubules and microcysts filled with abundant basophilic mucinous secretion and associated with a fibromyxoid stroma. The tumor cells were diffusely positive for CK7 and SOX10 and variably positive for S100 and p63. Breakapart fluorescence in situ hybridization for SS18 confirmed rearrangement of this gene. Together, these findings support a primary cutaneous MSA, presumably arising from ceruminous glands of the ear canal. Based on current knowledge of its salivary gland counterpart, cutaneous MSA is expected to be locally invasive but unlikely to recur or metastasize on complete excision.