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Abstract: Basal cell carcinoma (BCC) is the most common skin cancer, and it has numerous histologic mimics with variable prognoses and treatments. Although some immunohistochemical stains can be used for the differential diagnosis of BCC, variability and overlap in results can complicate their interpretation. Immunohistochemical staining for glioma-associated oncogene-1 (Gli-1) was performed on 26 nodular BCCs, 22 infiltrative BCCs, 9 basaloid squamous cell carcinomas, 12 desmoplastic trichoepitheliomas, 19 Merkel cell carcinomas, 11 sebaceous carcinomas, 10 cylindromas, 14 spiradenomas, 12 adenoid cystic carcinomas (AdCC), and 1 solitary trichoepithelioma. Strength of staining was scored as 0, 1+, 2+, or 3+, and distribution of staining was categorized as diffuse, multifocal, or focal. Strong, diffuse Gli-1 expression was seen in all tumors with basal epidermal-type differentiation, including BCC, trichoepithelioma, and basaloid squamous cell carcinoma. All examples of Merkel cell carcinoma were negative for cytoplasmic expression. Seven out of 11 sebaceous carcinomas were negative for Gli-1, and the remaining 4 showed 1+ expression. Cylindroma, spiradenoma, and AdCC, each an adnexal skin tumor, showed the most variable staining, but with cylindroma and spiradenoma demonstrating comparable labeling patterns. Overall, although Gli-1 may not distinguish between basal epidermal-type tumors, it may have a role in separating that group from lesions with adnexal differentiation, particularly sebaceous carcinoma, but also cylindroma, spiradenoma, and AdCC. Any cytoplasmic staining seems to exclude the diagnosis of Merkel cell carcinoma., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.)

Erythema multiforme (EM), Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN) comprise a family of mucocutaneous diseases associated with significant morbidity and mortality. Previous studies have confirmed the presence of autoantibodies to desmoplakin (Dp) I and II in patients with EM, SJS, and TEN. Truncated Dp production leads to characteristic changes visible on light microscopy: perinuclear clumping of keratin filaments and dyskeratotic keratinocyte. Based on these observations, the question arises as to whether a loss of Dp immunoreactivity in skin biopsies could serve as a diagnostic marker of EM, SJS, and TEN. This study analyzed Dp immunostaining patterns in 20 patients with EM or SJS/TEN. To assess the specificity of this approach, Dp immunostaining was also performed on specimens from patients with 5 potential histologic mimics of EM, SJS, and TEN. All of the samples from patients with EM, SJS, and TEN demonstrated absent or markedly diminished staining for Dp. A χ test demonstrated a statistically significant difference between the staining patterns in EM, SJS, and TEN and each of the other diagnostic groups that were investigated. This is the first report demonstrating statistically significant specificity of Dp staining patterns in EM/SJS/TEN as compared with other interface dermatitides.

Indeterminate dendritic cell tumor (IDCT) is a cutaneous proliferation of histiocytes that share morphologic and immunophenotypic properties with Langerhans cells. IDCT was recently included in the updated WHO classification of tumors of hematopoietic and lymphoid tissues. Recent studies have shown that some cases of IDCT demonstrate an ETV3-NCOA2 translocation, supporting the idea that IDCT is a clonal neoplasm. We report 2 new cases of IDCT at our institution lacking the ETV3-NCOA2 translocation. We also present a comprehensive review of reported cases of IDCT in the medical literature. Eighty-five cases of IDCT were reported in the literature between 1985 and 2016. The median age at diagnosis was 45 years. In contrast to Langerhans cell histiocytosis, IDCT is limited to the skin in the majority of cases (88%) and generally follows an indolent clinical course. Most reported lesions are cured with complete excision. However, the histologic features of IDCT and langerhans cell histiocytosis are similar. Conjoint immunostaining for CD1a and langerin is necessary for optimal classification.

Sclerosing squamous cell carcinoma (SCC), also known as "desmoplastic" SCC, is a rare subtype of cutaneous malignancy. This variant is clinically significant because it is associated with an increased risk of local recurrence and metastasis. We herein present 16 examples of sclerotic SCC of the skin in 8 men and 3 women, with a median age of 66 years. The most common site of origin for this tumor is the skin of the head and neck, including the scalp (5 tumors in 2 different patients), forehead (3 cases), nasal ala (2 cases), neck (2 cases in the same patient), ear (2 cases), cheek (1 case), and chest (1 case). Microscopically, sclerosing SCCs are characterized by cellular cords, nests, and islands, as well as scattered single cells infiltrating densely desmoplastic and collagenized connective tissue. The differential diagnosis principally includes sclerosing basal cell carcinoma, microcystic adnexal carcinoma, and desmoplastic trichoepithelioma. The main goals of this study are to further characterize these lesions pathologically, and increase general awareness of this SCC subtype.

Dermatopathology lost a giant in the field with the death of Philip H. Cooper, MD, on Friday, January 30, 2015. The following obituary represents a celebration of his life and his contributions to our field.

Distinction between radial growth phase (RGP) and vertical growth phase (VGP) in cutaneous melanomas is prognostically significant. Despite established morphological criteria, molecular markers to separate RGP and VGP have not been well established. The goal of this study was to investigate associations of p16, WT1, and Fli-1 with RGP-to-VGP progression, by immunohistochemistry. The p16 is a tumor suppressor, whereas WT1 and Fli-1 are transcriptional activators. The authors hypothesized that entry into VGP would be associated with decreased p16 and increased WT1 and Fli-1. Paraffin sections from 18 RGP and 15 VGP melanomas were immunostained with well-characterized antibodies to p16, WT1, and Fli-1. Melanoma growth phases were determined using precodified morphological attributes. In RGP melanomas, p16 was expressed in 15 of 18 (83%), WT1 in 17 of 17 (100%), and Fli-1 at least focally in 6 of 18 (33%). The deep dermal component of VGP melanomas stained positively for Fli-1 in 9 of 14 (64%), strongly for WT1 in 10 of 14 (71%), and strongly for p16 in only 2 of 15 (13%). Observed patterns of WT1 immunopositivity did not support the authors' hypothesis; it is not likely to be a good indicator of VGP. On the other hand, Fli-1 staining trended toward more positive deep tumor compartment staining and p16 to weaker staining in the deep compartment. At present, application of histological criteria remains the best method for assignment of growth phase in melanomas; however, p16 and possibly Fli-1 immunostains may serve as useful adjuncts in morphologically indeterminate cases.

Melanocytic nevus rests in lymph nodes are a known diagnostic challenge, especially in patients with a history of melanoma. Reticulin and NM23 have been studied in this context. The pattern of reticulin staining in melanomas surrounds groups/nests of melanocytes but individual cells in benign nevi. NM23, a metastasis-suppressor gene, has an association with metastatic potential in melanomas and some carcinomas. Twenty-eight cases (14 cases of metastatic melanoma to lymph nodes and 14 cases of lymph node nevus rests, all confirmed with Melan-A staining) were stained with reticulin and NM23. The pattern of reticulin staining was reported as surrounding groups if staining was noted in approximately 5-10 melanocytes in greater than 50% of the lesion but was otherwise reported as surrounding individual melanocytes. Cytoplasmic staining was considered to represent reactivity for NM23. Reticulin staining around groups of melanocytes was identified in all 14 cases of metastatic melanoma. Regarding nodal nevus rest cases, 12 of 14 cases (86%) demonstrated staining around individual melanocytes, whereas in 2 cases, reticulin surrounded melanocytic groups. NM23 staining was equivocal in all cases. Reticulin staining reliably invests groups of melanocytes in cases of metastatic melanoma, whereas in nodal nevus rests, it predominantly surrounds individual melanocytes. NM23 demonstrated no discriminatory value in this analysis. In cases in which a collection of melanocytes is present within a lymph node, reticulin deposition around individual melanocytes supports a diagnosis of lymph nodal nevus rest.

Oculocutaneous oncocytic tumors (OCOTs) are uncommon neoplasms that have been reported only rarely in the dermatopathology literature and whose immunophenotypic profile has not been well characterized. The clinical, histologic, and immunophenotypic features of 2 cases seen by the authors were assessed, and relevant publications in the literature were reviewed. Both patients with OCOTs were adult women with gradually enlarging, asymptomatic lesions involving the caruncle; they were locally excised. Histologically, the tumors were well-circumscribed nodules comprised of large oxyphilic cells arranged in confluent sheets and forming glandular spaces with secretory material. Microcystic areas and sparse intermingled goblet-cells were also apparent. Nuclear atypia and infiltrative growth were absent. Mitotic activity was absent in one case; a single mitotic figure was identified in the other. Immunostains demonstrated uniform expression of pankeratin and mitochondrial antigens. Both neoplasms were also labeled for markers associated with cutaneous adnexal, lacrimal, and minor salivary glandular tissue, including alpha-1-antitrypsin, gross cystic disease fluid protein-15, carcinoembryonic antigen, lysozyme and MUC1; each case expressed 4 of the 5 substances. Some cells expressed cytokeratins 5/6 and p63 consistent with the presence of basal-type differentiation in a subset of cells. No definite evidence of myoepithelial differentiation was demonstrated, as stains for smooth muscle actin, muscle-specific actin, and S100 protein were negative. Estrogen and progesterone receptor proteins were absent; strong cytoplasmic immunoreactivity for androgen receptor protein was evident, but nuclear staining was absent. The authors conclude that OCOTs show glandular differentiation. A review of the literature disclosed that none of these lesions arising in the caruncle behaved aggressively, in contrast to occasional tumors in other oculocutaneous sites.

Spindle cell proliferations of the skin are diverse, both morphologically and mechanistically. The authors have encountered four examples of a distinctive reactive/reparative cutaneous spindle cell lesion that shows homology with ones seen in the genitourinary tract and oral cavity and that is known as "postoperative/posttraumatic spindle cell nodule" (PSCN). These occurred in the skin of the face and scalp (2 cases), arm (1 case), and vulvar skin (one case), and were clearly related historically to prior episodes of trauma. The proliferations were characterized by variably-apposed and cytologically-bland spindle cells with numerous mitotic figures, set in a highly vascular stroma containing extravasated erythrocytes and inflammatory cells. All lesions were immunoreactive for vimentin, actin, and desmin, with no labeling for keratin. Postoperative/posttraumatic spindle cell nodule of the skin is a significant pseudoneoplastic lesion that is related (and perhaps identical pathogenetically) to nodular fasciitis; as such, it may be mistaken for a sarcoma or a spindle cell carcinoma. Careful attention to clinicopathologic and histologic details should result in its accurate recognition.

Five cases of solitary syringoma (SS) were found by the authors in a search of adnexal neoplasms seen over an 18-year period. These tumors all occurred in adults as mobile, flesh-colored, circumscribed papules of the facial skin, measuring < or = 5 mm in greatest dimension. Each was cured by simple punch or shave biopsy excision. Comparison with nine histologically similar variants of microcystic adnexal carcinoma (MAC) showed that the latter lesions differed from SS in that they showed much deeper invasion, with regular involvement of the underlying subcutis and perineural or vascular-adventitial infiltration. Moreover, SS was wider than it was deep on microscopic examination, whereas the converse pertained to MAC. Knowledge of the typical clinicopathologic attributes of these two tumor types should prevent clinicians and pathologists from confusing them with each other.

The sclerotic fibroma (SF) is a tumor of the skin that may occur sporadically or in the context of Cowden's syndrome. The authors studied four examples of this tumor in an effort to understand better the nature of the fibrous matrix in SF and its significance. A novel antibody was utilized that is directed against the immunoreactive amino-terminal precuror domain of human type I procollagen (AP). This peptide is usually identified only at sites of active or recent collagen synthesis and deposition. All examples of SF showed strong cellular and stromal staining for AP. The matrix also demonstrated variable staining for type IV collagen and laminin. The overall immunophenotype of this lesion suggests that it may be a specialized fibroblastic ("dermal dendrocytic?") tumor. Despite its hypocellularity and hyalinized nature, SF is thought to exhibit ongoing matrical production that supports a neoplastic character for this lesion.

A 70-year-old Italian man with a history of squamous cell carcinoma of the lung presented with a nodular skin eruption. He had traveled extensively in India and Sri Lanka. The nodules were well demarcated and measured up to 3.5 cm in diameter. Histologically, there was a proliferation of spindled and polygonal cells with focal and relatively inconspicuous cytoplasmic vacuolation. A macrophage-monocyte lineage for the cells was confirmed by paraffin section immunohistochemistry, using the monoclonal antibodies anti-CD45, MAC-387, KP-1, UCHL-1, MT-1, L26, and MB2. Infiltrating borders, extension of the lesion into the subcutis, and involvement of small dermal nerves and eccrine glands initially suggested the possibility of a "histiocytic" neoplasm of indeterminate biological potential. However, air-dried and Giemsa-stained material from a fine-needle aspirate of one cutaneous nodule showed needle-shaped intracellular "negative images," and acid-fast stains revealed a large number of intracytoplasmic bacilli in virtually all of the vacuolated lesional cells. Furthermore, a second skin nodule that was excised 3 weeks after initial presentation showed the typical morphology of lepromatous leprosy. The clinicopathologic features of this case demonstrated several similarities with those of so-called "histoid" leprosy. Unusual morphologic variants of leprosy need to be considered in the interpretation of unusual "histiocytic" infiltrates in order to avoid a mistaken diagnosis of neoplasia, regardless of the geographic locale in which the patient is evaluated.

Pilomatrixoma, a neoplasm of hair germ matrix origin, is one of the most common cutaneous appendage tumors in patients 20 years of age or younger. Our review of cutaneous adnexal tumors in the first 2 decades of life showed that pilomatric lesions accounted for approximately 75% of cases. We examined 76 tumors from 69 patients between the ages of 8 months and 19 years (average age, 8 years). The female-to-male ratio was 3:1. We noted a predilection for the head and neck region, as has also been reported by other investigators. Sixty-nine tumors were examples of typical or classic pilomatrixoma; four of them showed the unusual histologic feature of transepidermal elimination or perforation. None of the tumors in the typical category recurred during a follow-up period that averaged 8.7 years. Seven of the lesions with atypical histologic features were examples of aggressive pilomatrixoma (three cases) and pilomatrical carcinoma (four cases). The average age of these seven patients was similar to that of the overall group. The pilomatrical carcinomas were characterized by invasive nests of tumor cells with irregular borders, large vesicular nuclei, prominent nucleoli, multiple mitotic figures, and focal necrosis. A desmoplastic stroma surrounded the infiltrating nests of tumor. Two of the four pilomatrical carcinomas recurred 2 and 6 months, respectively, after initial excision. The aggressive pilomatrixomas had a similar infiltrative growth pattern, but they did not exhibit the same degree of worrisome cytologic features. Single cell necrosis, identifiable mitotic figures, and prominent nucleoli differentiated the atypical from the typical pilomatrixomas. One of the three aggressive pilomatrixomas recurred after 2 months.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical and light-microscopic findings were reviewed in 60 benign histiocytic tumors of the skin arising in patients who were 19 years of age or younger. These lesions were placed in five categories, based on the presence or absence of Touton giant cells, the relative content of vacuolated polygonal cells and spindle cells, and the extent of stromal collagen in the proliferations. The resulting distribution included 16 cases of classic juvenile xanthogranuloma (JXG), four examples of xanthomatous JXG, 11 "transitional" JXG, 11 histiocytomas, and 18 dermatofibromas. The histological appearances of the lesions were related to the elapsed time between their clinical presentation and biopsy sampling. Intervals of 3.5, 3.5, 3.6, 7, and 13.4 months were noted for each histologic group, respectively. Hence, "early" lesions (JXG variants) showed no differences in clinical duration, but significantly longer evolutions were observed for histiocytomas and dermatofibromas. Immunohistochemical studies were conducted utilizing antibodies to several "histiocytic" markers (CD68, cathepsin B, MAC387), CD45 antigen, and S-100 protein. Cathepsin B was universally expressed by all tumors, but its intensity and scope were variable. In addition, only dermatofibromas failed to show CD68 positivity. Scattered mononuclear inflammatory cells in the lesions were CD45 reactive, whereas other cell types were not so labeled. MAC387 was absent in all cases. These findings suggest that these lesions do indeed show histiocytic differentiation, and that they are probably related to peripheral blood monocytes antigenically. Differences in the histologic appearances of these cutaneous histiocytic proliferations of childhood may simply reflect dissimilar periods of clinical growth before biopsies are performed.

Adnexal carcinomas of the skin are rare lesions that encompass multiple histologic patterns. The authors have identified seven neoplasms in this category that showed combined morphologic features of at least two appendegeal tissues. Two manifested pilar and sebaceous differentiation, three showed pilar, sebaceous, and sudoriferous features, and two had sweat glandular and sebaceous characteristics. All tumors arose in the skin of the head and neck; four patients were men and three were women (age range, 21-84 years). One lesion had been present for 25 years with progressive enlargement over the last 3, and another two had slowly expanded over 1-2 years; the duration of growth for the remaining cases was uncertain. Follow-up revealed that six patients were free of disease for at least 1 year after complete excision. In the seventh case, complete excision was performed, but follow-up was not available. Immunohistochemical analysis showed reactivity for keratin and epithelial membrane antigen in each case. Carcinoembryonic antigen was seen in four tumors, and amylase was present in three; none expressed vimentin, S100 protein, or gross cystic disease fluid protein-15. It is concluded that mixed cutaneous adnexal carcinomas are recognizable entities that appear to have little potential for aggressive growth. Immunohistochemical studies may serve as adjuncts to conventional microscopy in the definition of cellular lineages pursued by such neoplasms.

Neuroendocrine differentiation in basal cell carcinoma (BCC) of the skin has been reported in the past on the basis of ultrastructural findings, argyrophilia, and the immunohistochemical detection of neuropeptides in such neoplasms. To assess further the relative frequency of neuroendocrine differentiation in BCC, paraffin sections of 53 randomly chosen cases were evaluated for Churukian-Schenk stain positivity and the expression of sensitive neuroendocrine markers. These included neuron-specific enolase (using a highly absorbed monospecific antiserum), chromogranin-A, synaptophysin, neurofilament protein, and Leu-7 antigen. Although 25% of cases demonstrated argyrophilia with the Churukian-Schenk method, suggesting a high frequency of possible neuroendocrine differentiation, immunohistochemical evidence of the same was observed in only two tumors (4%). These demonstrated immunoreactivity for chromogranin and neuron-specific enolase. The results of this analysis suggest that neuroendocrine differentiation in BCC is relatively uncommon, and that it is not reliably predicted by the results of argyrophil stains done on paraffin sections.

We herein report two cases of sweat gland carcinoma that arose in association with eccrine spiradenoma. These lesions presented as enlarging masses that previously had been stable for many years. One produced widespread metastasis and death 5 months after diagnosis. Immunohistochemical studies demonstrated an antigenic relationship between the benign and malignant components of sweat gland carcinoma ex eccrine spiradenoma, but ultrastructural analyses showed a paucity of specialized differentiation. This neoplasm appears to display a range of microscopic appearances and has proven fatal in 20% of reported cases.

Atypical fibroxanthoma belongs to the family of spindle-cell and pleomorphic neoplasms of the skin. The lineage of differentiation of this tumor and the means whereby it can be diagnostically separated from other similar morphologic entities have been controversial. In order to address these issues, the authors studied 30 spindle-cell and/or pleomorphic cutaneous tumors, including atypical fibroxanthomas (AFXs), superficial malignant fibrous histiocytomas (MFHs), dermatofibrosarcoma protuberans (DFSPs), sarcomatoid squamous-cell carcinomas (SCCs), spindle-cell malignant melanomas (MMs), and leiomyosarcomas, (LMSs). These cases were analyzed using a panel of eight antibodies and the immunoperoxidase technique. AFXs were reactive for vimentin, alpha-1-antichymotrypsin (AACT), alpha-1-antitrypsin (AAT), and cathepsin-B (CB) but failed to display cytokeratin (CK), epithelial membrane antigen (EMA), S-100 protein, and desmin. MFHs and DFSPs exhibited immunophenotypic profiles that were nearly identical to that just described. In contrast, SCCs were typified by positivity for CK and EMA; MMs exhibited uniform reactivity for S-100 protein; and LMSs contained desmin in four of five cases. A surprising result was the expression of S-100 by LMSs. Also, all tumors displayed at least one of the three proteolytic enzymes assessed in this study (AAT, AACT, and CB), demonstrating the relative diagnostic nonspecificity of these determinants. It is concluded that AFXs are "fibrohistiocytic" neoplasms, with substantial morphologic and immunohistochemical similarity to MFHs. The immunohistochemical classification of spindle-cell and pleomorphic tumors of the skin necessitates the use of antibody panels to assess the presence of markers that are characteristic of each diagnostic group.

We report two cases of cutaneous malignant peripheral nerve sheath tumors. One occurred in a patient without neurofibromatosis and manifested as a recurrent scalp nodule. Histologically, the lesion began as a benign-appearing, dermal neurofibroma and progressed to a highly cellular, pleomorphic neoplasm with prominent mitotic activity and invasion of the subcutis. Immunohistochemical and ultrastructural examination confirmed the nerve sheath origin of this tumor. The other case presented as a large scalp mass in a patient with an established diagnosis of neurofibromatosis; its immunohistochemical characteristics were identical to those of case 1. Although malignant peripheral nerve sheath tumors are uncommon in the skin, they can be effectively separated from other spindle cell neoplasms by specialized pathologic studies.

An adenoid cystic carcinoma of the skin was compared with three similar neoplasms of salivary glands and with an adenoid basal cell carcinoma, from unrelated cases. The histological and immunocytochemical details of these tumors were analyzed in an attempt to determine whether or not their differing clinical behaviors would be reflected in pathologic dissimilarities. Although the single adenoid cystic carcinoma of the skin did not recur or metastasize over a 10-year follow-up period, its morphologic and biochemical features were identical to those of biologically aggressive salivary gland tumors. All four adenoid cystic carcinomas contained carcinoembryonic antigen, epithelial membrane antigen, salivary-type amylase, and alpha-lactalbumin, and all bound peanut agglutinin. Three of four expressed positivity for S100 protein, and two contained low-molecular-weight cytokeratin. In contrast, none was immunoreactive for beta-2-microglobulin, and only one displayed blood group isoantigen positivity. The adenoid basal cell carcinoma was negative for all immunological determinants, but it bound peanut agglutinin. Although these results should be regarded as preliminary, it appears that adenoid cystic carcinoma is a pathologically distinct and uniform entity, whether it occurs in the skin or in salivary glands. However, the clinical behavior of this tumor cannot be predicted on the basis of immunohistochemical or morphological studies. Finally, adenoid basal cell carcinoma is histopathologically and immunocytochemically separable from cutaneous adenoid cystic carcinoma.

The eruption of multiple lobular capillary hemangiomas (granulomata pyogenicum) is a previously documented but uncommon phenomenon. Reported cases have featured the recurrence of multiple satellite lesions after surgical removal of, or trauma to, a solitary capillary hemangioma. Sporadic cases of multifocal lesions arising de novo in both previously traumatized and uninjured skin have been described as well. We describe herein two unusual patients with disseminated lobular capillary hemangioma. One patient developed skin nodules in several sites, including the mouth, knee, thumb, and foot, after surgical removal of a solitary oculocutaneous neoplasm. The second patient had more than 700 skin lesions, distributed over the entire body. Unlike those in most previously reported examples of this condition, these two patients were elderly. Both were misdiagnosed clinically as having malignant vascular neoplasms, but the behavior of the lesions was benign, despite conservative surgical excisions in one patient and relative lack of therapeutic intervention in the other.

Although leukocyte common antigen is a valuable discriminant between lymphoreticular proliferations and other histologically similar neoplasms, several publications have described difficulties in adequately labeling this determinant in formalin-fixed, paraffin-embedded tissues. We studied 662 paraffinized cutaneous and noncutaneous neoplasms for the presence of leukocyte common antigen, using an extended avidin-biotin-peroxidase complex (ABC) method, a combined ABC-peroxidase-antiperoxidase technique, and a biotin-strept-avidin procedure. Each of the three immunohistochemical techniques produced effective results in the detection of leukocyte common antigen in all malignant lymphomas, but none of them produced false-positive staining in nonhematopoietic lesions. These results suggest that antibodies to leukocyte common antigen are highly specific and that the methods employed in this study allow for excellent diagnostic sensitivity in the recognition of cutaneous lymphomas.