Primary cutaneous marginal zone lymphoproliferative disorder following COVID-19 vaccination.

During the coronavirus disease 2019 (COVID-19) pandemic, COVID-19 vaccines were administered worldwide. A number of skin reactions, including primary cutaneous T-cell lymphoproliferative disorders (LPDs) were reported following COVID-19 vaccination. We report a case of primary cutaneous marginal zone lymphoproliferative disorder (PCMZLPD) secondary to COVID-19 vaccination. A 57-year-old man presented with an erythematous nodule on his left arm at the site of vaccine inoculation following his first dose of the Moderna (mRNA-1273) vaccine a few weeks prior. The nodule continued to progress in size after the second dose. A skin biopsy specimen of the nodule showed a diffuse dermal infiltrate of small to medium-sized lymphocytes with plasma cells and histiocytes. The infiltrate was composed of CD3+ T cells with CD20+ and CD79a+ B cells. The neoplastic B cells reacted with BCL-2 and were negative for BCL-6 and CD10. Kappa light chain restriction was identified by in situ hybridization. Gene rearrangement studies revealed kappa light chain monoclonality, confirming the diagnosis of PCMZLPD. The temporal association with the Moderna vaccination and the occurrence of the lesion at the inoculation site indicate a COVID-19 vaccination-induced PCMZLPD. This is one of the rare cases of PCMZLPD following COVID-19 vaccination.

Cutaneous Kaposi Sarcoma as a Presenting Sign of HIV: A Case Report.

We present the case of a 68-year-old man with no known risk factors for HIV infection who developed a new, rapidly growing lesion on the left medial foot. The lesion was biopsied and found to be consistent with Kaposi sarcoma (KS). He subsequently tested positive for HIV and developed cellulitis of the left lower extremity. Treatment involved empiric antibiotics, surgical excision of the lesion, radiation therapy, and antiretroviral therapy. The development of KS with no known history of HIV/AIDS is uncommon, with only a few reported cases. We provide a summary of 18 cases in the current literature of cutaneous KS as an initial presenting sign of HIV/AIDS.

Epithelioid hemangioma involving large arteries in the skin.

Epithelioid hemangioma (EH) is a benign vascular lesion, typically consisting of small vascular channels lined by epithelioid endothelial cells and associated with a dense lymphocytic infiltrate with eosinophils. Here, we report a rare case of EH involving large arteries. The patient presented with a 9-month history of an asymptomatic nodule on the forehead, which was thought to be an epidermal inclusion cyst. Skin biopsy revealed large arteries with clusters of epithelioid cells in the vascular walls and lumen. Scattered eosinophils were noted in the walls. Adjacent areas showed groups of small-caliber vessels lined by prominent endothelial cells and associated with a dense lymphoid infiltrate with eosinophils. No significant cytologic atypia was noted. Given the presence of the classic small-vessel involvement, along with CD31 reactivity for the epithelioid cells in the large vessels, the findings are classified as EH involving large arteries, which is an uncommon subtype. There have only been a handful of such cases reported in the literature.

Cutaneous basal cell carcinosarcomas: evidence of clonality and recurrent chromosomal losses.

Cutaneous carcinosarcomas are heterogeneous group of tumors composed of malignant epithelial and mesenchymal components. Although mutation analyses have identified clonal changes between these morphologically disparate components in some subtypes of cutaneous carcinosarcoma, few cases have been analyzed thus far. To our knowledge, copy number variations (CNVs) and copy-neutral loss of heterozygosity (CN-LOH) have not been investigated in cutaneous carcinosarcomas. We analyzed 4 carcinosarcomas with basal cell carcinoma and osteosarcomatous components for CNVs/CN-LOH by comparative genomic hybridization/single-nucleotide polymorphism array, TP53 hot spot mutations by polymerase chain reaction and Sanger sequencing, and TP53 genomic rearrangements by fluorescence in situ hybridization. All tumors displayed multiple CNV/CN-LOH events (median, 7.5 per tumor). Three of 4 tumors displayed similar CNV/CN-LOH patterns between the epithelial and mesenchymal components within each tumor, supporting a common clonal origin. Recurrent changes included allelic loss at 9p21 (CDKN2A), 9q (PTCH1), and 17p (TP53). Allelic losses of chromosome 16 including CDH1 (E-cadherin) were present in 2 tumors and were restricted to the sarcomatous component. TP53 mutation analysis revealed an R248L mutation in both epithelial and mesenchymal components of 1 tumor. No TP53 rearrangements were identified. Our findings indicate that basal cell carcinosarcomas harbor CNV/CN-LOH changes similar to conventional basal cell carcinoma, with additional changes including recurrent 9p21 losses and a relatively high burden of copy number changes. In addition, most cutaneous carcinosarcomas show evidence of clonality between epithelial and mesenchymal components.

CD34-positive superficial myxofibrosarcoma: a potential diagnostic pitfall.

BACKGROUND: Myxofibrosarcoma (MFS) arises most commonly in the proximal extremities of the elderly, where it may involve subcutaneous and dermal tissues and masquerade as benign entities in limited biopsy samples. We encountered such a case, in which positivity for CD34 and morphologic features were initially wrongly interpreted as a 'low-fat/fat-free' spindle cell/pleomorphic lipoma. Case series have not assessed prevalence of CD34 reactivity among cutaneous examples of MFS. METHODS: We performed a systematic review of our institution's experience, selecting from among unequivocal MFS resection specimens those superficial cases in which a limited biopsy sample might prove difficult to interpret. These cases were immunostained for CD34 and tabulated for clinicopathologic characteristics. RESULTS: After review of all MFS diagnoses over 5 years (n = 56), we identified a study group of superficial MFS for comparison to the index case (total n = 8). Of these, the index and three additional cases (4 of 8, 50%; 2 low, 2 high grade) demonstrated positive staining for CD34, with diffuse staining of spindled cells including cellular processes. Four additional cases showed no or equivocal/rare staining. CONCLUSIONS: CD34 positivity should be recognized as prevalent among such cases and should not be inappropriately construed as inveighing against a diagnosis of MFS in favor of benign entities.

DEK expression in Merkel cell carcinoma and small cell carcinoma.

BACKGROUND: The chromatin architectural factor DEK maps to chromosome 6p and is frequently overexpressed in several neoplasms, including small cell lung carcinoma, where it is associated with poor prognosis, tumor initiation activity and chemoresistance. DEK expression has not been studied in cutaneous Merkel cell carcinoma. METHODS: We applied a DEK monoclonal antibody to 15 cases of Merkel cell carcinoma and 12 cases of small cell carcinoma. DEK nuclear immunoreactivity was scored based on percentage (0, negative; 1+, <25%; 2+, 25-50%; 3+, >50%) and intensity (weak, moderate or strong). RESULTS: All 15 Merkel cell carcinoma cases (100%) showed diffuse (3+) nuclear positivity (14 strong, 1 weak). Six of 12 small cell carcinoma cases (50%) showed diffuse (3+) and strong nuclear positivity, while one case exhibited focal (1+) weak nuclear positivity. The remaining five cases were negative for DEK expression. CONCLUSIONS: Our results suggest that DEK may be involved in the pathogenesis of Merkel cell carcinoma and therefore may provide therapeutic implications for Merkel cell carcinomas. In addition, the difference in DEK expression between Merkel cell carcinoma and small cell carcinoma suggests possible separate tumorigenesis pathways for the two tumors.

Sebaceous neoplasms with mismatch repair protein expressions and the frequency of co-existing visceral tumors.

BACKGROUND: Visceral malignancy has been associated with sebaceous neoplasms in patients with Muir-Torre syndrome. However, no large studies have been done to evaluate the frequency of visceral tumors in patients with sebaceous neoplasms and mismatch repair (MMR) protein expression of the sebaceous tumors. OBJECTIVE: We sought to determine the frequency of visceral tumors in patients with sebaceous neoplasms, MMR protein expression of the sebaceous tumors, and the related surveillance practices of physicians. METHODS: We identified 85 patients with sebaceous neoplasms. Relevant clinical information was obtained via chart review and database searches. MMR protein expression was examined by immunohistochemistry. RESULTS: Nineteen of the 85 patients had a total of 22 visceral malignancies, of which 41% were genitourinary in origin. Ten of the 17 patients (59%) with visceral malignancy had loss of MMR expression in their sebaceous neoplasms or somatic MMR mutation. Thirty patients had other findings such as colonic adenomas and polyps. Of the 23 patients who had a family history of visceral malignancy, 9 had a personal history of visceral malignancy. LIMITATIONS: Only one sebaceous tumor from each patient (except one) was tested for MMR, which might reduce the sensitivity. CONCLUSION: Our findings demonstrate an increased frequency of internal malignancy in patients with sebaceous neoplasms compared with the general population, and highlight the heterogeneous nature of the visceral tumors. A majority of the sebaceous tumors show loss of MMR expression. The study reminds us to strive toward a consistent and comprehensive approach to screening for internal malignancy when a patient is given a diagnosis of a sebaceous neoplasm.

Cutaneous Richter syndrome: report of 3 cases from one institution.

BACKGROUND: Richter syndrome (RS) is large-cell transformation of chronic lymphocytic leukemia (CLL). It commonly involves lymph nodes and bone marrow, but may rarely manifest in skin. Certain triggering factors, such as Epstein-Barr virus infection and p53 overexpression, have been implicated in the pathogenesis of RS. Here, we present 3 cases of cutaneous RS from our institution with a follow-up period of up to 8 years. OBJECTIVE: We present a series of cutaneous RS from a single institution with the longest follow-up period (up to 8 years) to date. METHODS: Clinical characteristics were collected and histopathological findings of skin biopsy specimens were analyzed. RESULTS: All 3 patients had prior CLL and later developed cutaneous RS lesions. The mean age at the diagnosis of cutaneous RS was 67 years old. The time intervals between CLL and cutaneous RS were 3 to 8 years. Skin biopsy specimens demonstrated dermal nodular or perivascular infiltrates of large B cells, showing similar immunophenotypes to the lesional cells in the original CLL. Overexpression of p53 and positive stain for Epstein-Barr virus--encoded small RNA was found in one patient. One patient remained alive 8 years after the diagnosis whereas the other two died of the disease at 5 years and 3 weeks, respectively, after the onset of cutaneous RS. LIMITATIONS: Three patients with RS were followed up for up to 8 years. CONCLUSIONS: Our findings suggested that, in contrast to extracutaneous RS, cutaneous RS generally has a less aggressive course with longer survival unless other worse prognostic factors are present.

DEK expression in melanocytic lesions.

The diagnosis of malignant melanoma presents a clinical challenge and relies principally on histopathological evaluation. Previous studies have indicated that increased expression of the DEK oncogene, a chromatin-bound factor, could contribute to the development of melanoma and may be a frequent event in melanoma progression. Here, we investigated DEK expression by immunohistochemistry in a total of 147 melanocytic lesions, including ordinary nevi, dysplastic nevi, Spitz nevi, melanoma in situ, primary invasive melanomas, and metastatic melanomas. Most benign nevi (ordinary, dysplastic, and Spitz nevi) were negative or exhibited weak staining for DEK, with only 4 of 49 cases showing strong staining. Similar to benign nevi, melanoma in situ also demonstrated low levels of DEK expression. In contrast, the expression of DEK in primary invasive melanomas was significantly higher than benign nevi (P < .0001). Moreover, DEK expression was significantly increased in deep melanomas (Breslow depth >1 mm) and metastatic melanomas as compared with superficial melanomas (Breslow depth ≤1 mm) (P < .05). Our findings indicate that DEK overexpression may be a frequent event in invasive melanomas, and further augmentation of DEK expression may be associated with the acquisition of ominous features such as deep dermal invasion and metastasis. These data suggest a role of DEK in melanoma progression.

Specificity of IRF4 translocations for primary cutaneous anaplastic large cell lymphoma: a multicenter study of 204 skin biopsies.

Current pathologic criteria cannot reliably distinguish cutaneous anaplastic large cell lymphoma from other CD30-positive T-cell lymphoproliferative disorders (lymphomatoid papulosis, systemic anaplastic large cell lymphoma with skin involvement, and transformed mycosis fungoides). We previously reported IRF4 (interferon regulatory factor-4) translocations in cutaneous anaplastic large cell lymphomas. Here, we investigated the clinical utility of detecting IRF4 translocations in skin biopsies. We performed fluorescence in situ hybridization (FISH) for IRF4 in 204 biopsies involved by T-cell lymphoproliferative disorders from 182 patients at three institutions. In all, 9 of 45 (20%) cutaneous anaplastic large cell lymphomas and 1 of 32 (3%) cases of lymphomatoid papulosis with informative results demonstrated an IRF4 translocation. Remaining informative cases were negative for a translocation (7 systemic anaplastic large cell lymphomas; 44 cases of mycosis fungoides/Sézary syndrome (13 transformed); 24 peripheral T-cell lymphomas, not otherwise specified; 12 CD4-positive small/medium-sized pleomorphic T-cell lymphomas; 5 extranodal NK/T-cell lymphomas, nasal type; 4 gamma-delta T-cell lymphomas; and 5 other uncommon T-cell lymphoproliferative disorders). Among all cutaneous T-cell lymphoproliferative disorders, FISH for IRF4 had a specificity and positive predictive value for cutaneous anaplastic large cell lymphoma of 99 and 90%, respectively (P=0.00002, Fisher's exact test). Among anaplastic large cell lymphomas, lymphomatoid papulosis, and transformed mycosis fungoides, specificity and positive predictive value were 98 and 90%, respectively (P=0.005). FISH abnormalities other than translocations and IRF4 protein expression were seen in 13 and 65% of cases, respectively, but were nonspecific with regard to T-cell lymphoproliferative disorder subtype. Our findings support the clinical utility of FISH for IRF4 in the differential diagnosis of T-cell lymphoproliferative disorders in skin biopsies, with detection of a translocation favoring cutaneous anaplastic large cell lymphoma. Like all FISH studies, IRF4 testing must be interpreted in the context of morphology, phenotype, and clinical features.

Atypical fibroxanthoma with lymphomatoid reaction.

BACKGROUND: Atypical fibroxanthoma (AFX) represents an uncommon skin tumor typically occurring on sun-damaged skin of the elderly. Histopathologic variants include spindled, clear cell, osteoid, osteoclastic, chondroid, pigmented, granular cell and myxoid lesions. To date, an atypical lymphoid infiltrate, including CD30-positive large cells mimicking lymphomatoid papulosis, has not been described in association with AFX. METHODS: The clinical and histopathological characteristics of two AFX cases inciting an atypical lymphoid infiltrate, along with immunohistochemical profiles and T-cell receptor gamma (TCRγ) gene rearrangement results, were reviewed. RESULTS: Lesions in both cases occurred as solitary nodules in elderly patients. Microscopically, both lesions showed a cellular proliferation composed of pleomorphic spindle cells, associated with a prominent intralesional atypical lymphoid infiltrate. The spindle cells expressed CD10 but lacked the expression of S-100, cytokeratins and muscle markers, thereby confirming the diagnosis of AFX. CD30 highlighted a significant subset of large mononuclear cells in the lymphoid infiltrate of one case. TCRγ gene rearrangement analyses were negative for both cases. CONCLUSION: An atypical lymphoid infiltrate, including the one resembling lymphomatoid papulosis, associated with AFX has not been previously described. It is important to recognize the reactive nature of the infiltrate to avoid a misdiagnosis of lymphoma.

From melanocyte to metastatic malignant melanoma.

Malignant melanoma is one of the most aggressive malignancies in human and is responsible for almost 60% of lethal skin tumors. Its incidence has been increasing in white population in the past two decades. There is a complex interaction of environmental (exogenous) and endogenous, including genetic, risk factors in developing malignant melanoma. 8-12% of familial melanomas occur in a familial setting related to mutation of the CDKN2A gene that encodes p16. The aim of this is to briefly review the microanatomy and physiology of the melanocytes, epidemiology, risk factors, clinical presentation, historical classification and histopathology and, more in details, the most recent discoveries in biology and genetics of malignant melanoma. At the end, the final version of 2009 AJCC malignant melanoma staging and classification is presented.

Expression of the embryonic morphogen Nodal in cutaneous melanocytic lesions.

Nodal, a potent embryonic morphogen in the transforming growth factor-beta family, is a proposed key regulator of melanoma tumorigenicity. However, there has been no systematic study of Nodal expression in melanocytic lesions. We investigated Nodal expression by immunohistochemistry in 269 melanocytic lesions, including compound nevi, dysplastic nevi, congenital nevi, Spitz nevi, melanoma in situ, malignant melanoma including the variant desmoplastic melanoma, and metastatic melanoma. We found that the Nodal expression was significantly increased in malignant lesions (including melanoma in situ, malignant melanoma, and metastatic melanoma) compared with compound nevi, Spitz nevi, and dysplastic nevi. Surprisingly, congenital nevi expressed a level of Nodal comparable with malignant lesions, whereas desmoplastic melanoma showed lower expression than nondesmoplastic malignant melanoma (P<0.05). Deep melanoma (Breslow depth >1 mm) displayed a higher percentage of Nodal-positive tumor cells than did superficial melanoma (Breslow depth < or =1 mm), although there was no statistical difference in the overall staining intensity (P=0.18). Melanomas in situ showed a lower level of Nodal expression than did deep melanomas and metastatic melanomas (P<0.05). The low expression of Nodal in normal and dysplastic nevi, and its increasing expression with the progression of malignant lesions, are suggestive of a role for Nodal in melanoma progression.

CD163 expression in leukemia cutis.

BACKGROUND: Proper diagnosis of myeloid leukemia cutis (LC) is of great clinical importance but can be difficult because no single immunohistochemical marker is adequately sensitive or specific for definitive diagnosis. Thus, a broader panel of markers is often desirable. CD163 is highly specific for normal and neoplastic cells of the monocyte/histiocyte lineage. In this study, we examined the value of CD163 in the diagnosis of acute myeloid LC. METHODS: A total of 34 cases, including 18 cases of myelomonocytic or monocytic LC, 10 cases of myeloid LC without monocytic component and 6 cases of acute lymphoblastic leukemia/lymphoma (ALL), were stained with CD163. RESULTS: CD163 was expressed in 8 of 18 (44%) of myelomonocytic or monocytic LC and 1 of 10 (10%) of other myeloid LC, but in none of the ALL cases (0/6). CD163 was highly specific (90%) for myeloid LC with a monocytic component, but showed low sensitivity in the diagnosis of both myeloid LC in general (24%) and myeloid LC with a monocytic component (44%). CONCLUSIONS: Our results suggest that CD163 has utility as a specific marker for myeloid LC in conjunction with currently used immunohistochemical stains, but should not be used alone for diagnosis.

D2-40, a novel immunohistochemical marker in differentiating dermatofibroma from dermatofibrosarcoma protuberans.

The distinction between dermatofibroma, particularly cellular variant, and dermatofibrosarcoma protuberans in excisional biopsies is usually straightforward. However, a separation between the two may be sometimes challenging, especially in superficial biopsies. Although factor XIIIa and CD34 immunostains are useful in differentiating dermatofibroma and dermatofibrosarcoma protuberans in most instances, focal CD34 positivity may be seen in cellular fibrous histiocytoma. Some cases reveal overlapping immunostain results. D2-40 identifies a 40-kDa O-linked sialoglycoprotein present on a variety of tissues including testicular germ cell tumors as well as lymphatic endothelium. In this study, we investigated the utility of D2-40 in separating dermatofibroma from dermatofibrosarcoma protuberans and compared the results with other commonly used immunostains. Fifty-six cases of dermatofibroma (including six cellular variant) and 29 cases of dermatofibrosarcoma protuberans were retrieved from the archives of Department of Anatomic Pathology at Sunnybrook Health Sciences Center in University of Toronto. We applied factor XIIIa, CD34, and monoclonal mouse anti-D2-40 immunostains to formalin-fixed, paraffin-embedded tissue sections. All 56 (100%) cases of dermatofibroma demonstrated strong and diffuse immunoreactivity to D2-40 in the spindle cells and stroma. Similarly, factor XIIIa showed strong and diffuse positivity in the spindle cells. Nearly all dermatofibromas were negative for CD34 except one case revealing focal positivity. None of dermatofibrosarcoma protuberans cases were labeled by D2-40, although four cases showed weak and patchy background staining in contrary to diffuse, strong, and crisp staining seen in dermatofibromas. Our results indicate that D2-40 seems to be a sensitive immunohistochemical marker for dermatofibromas, including cellular variant. Focal and faint D2-40 staining may be seen in the stroma of dermatofibrosarcoma protuberans. Our findings suggest that D2-40 can be used as a complementary immunostain to factor XIIIa and CD34 in problematic and challenging cases on superficial biopsies.

IMP-3 expression in melanocytic lesions.

BACKGROUND: Insulin-like growth factor-II mRNA-binding protein 3 (IMP-3 ), a member of the insulin-like growth factor mRNA-binding protein family, is expressed in several human malignancies, including melanomas. However, the expression of IMP-3 has not been explored in melanoma in situ, various histologic subtypes of invasive melanomas and atypical Spitz tumors. METHODS: IMP-3 immunostain was performed in 157 melanocytic lesions. RESULTS: Nearly all benign (8/8), dysplastic (8/8) and Spitz nevi (8/9) were negative for IMP-3. Focal IMP-3 positivity was observed in 5/12 melanoma in situ and 4/15 superficial melanomas (Breslow depth 1 mm) and 25/52 metastatic melanomas demonstrated strong IMP-3 staining. IMP-3 expression differs significantly between non-desmoplastic melanomas (superficial and deep) and benign or dysplastic or Spitz nevi (p = 0.0427, respectively). Four of 23 desmoplastic melanomas expressed IMP-3 , which was significantly different from deep melanomas (p = 0.0109). IMP-3 stained 7 of 10 atypical Spitz tumors. The difference between atypical Spitz tumors and Spitz nevi was statistically significant (p = 0.0256). CONCLUSION: A malignant circumstance, such as non-desmoplastic melanoma or atypical Spitz tumor, can be inferred when IMP-3 is expressed, suggesting potential diagnostic value of IMP-3 in melanocytic lesions.

Diagnostic utility of IMP3 in segregating metastatic melanoma from benign nevi in lymph nodes.

Depending on the Breslow depth of the primary melanoma, sentinel lymph node biopsy is considered as standard of care for the staging of cutaneous melanoma, and is one of the most important prognostic factors. The histologic analysis of these specimens becomes difficult to interpret when benign intranodal nevic cells mimic metastases. Insulin-like growth factor-II messenger RNA (mRNA)-binding protein-3 (IMP3), also known as K homology domain-containing protein overexpressed in cancer or L523S, is a member of the insulin-like growth factor-II mRNA-binding protein family and has been shown to have diagnostic utility in distinguishing cutaneous melanoma from benign nevi. In this study, 43 sentinel lymph node biopsy specimens, including 13 with benign intranodal nevi and 30 with metastatic melanoma (two cases containing both benign nevi and metastatic melanoma), from 41 patients were immunohistochemically analyzed with a monoclonal antibody against IMP3. None of the benign intranodal nevi expressed IMP3, whereas 21 out of 30 (70%) of the lymph nodes containing metastatic melanoma did. It seems that IMP3 is helpful in distinguishing benign intranodal nevi from metastatic melanoma in sentinel lymph node biopsy specimens, and could be a valuable diagnostic adjunct in sentinel lymph node biopsy assessment in which questions arise as to the malignancy of the melanocytes present.

Clusterin expression in cutaneous CD30-positive lymphoproliferative disorders and their histologic simulants.

BACKGROUND: Clusterin is a ubiquitous 80 kDa heterodimeric glycoprotein previously shown to be expressed on tumor cells of systemic and, to a lesser extent, primary cutaneous anaplastic large cell lymphoma (PC-ALCL). Lymphomatoid papulosis (LyP), an important differential diagnosis of ALCL, has been studied for clusterin expression in only a small number of cases. The aim of this study was to compare clusterin immunostaining patterns in LyP and other cutaneous histologic simulants with those of PC-ALCL. METHODS: Formalin-fixed, paraffin-embedded sections of PC-ALCL (6), LyP (20), mycosis fungoides with large cell transformation (MF-LCT, 12), pityriasis lichenoides et varioliformis acuta (PLEVA, 12), arthropod bite reaction (ABR, 12) and lymphomatoid reactions (LR, 9) were immunostained for clusterin and evaluated for staining pattern and distribution. All diagnoses were made with clinicopathologic correlation. RESULTS: Characteristic dot-like Golgi staining was identified in 10/20 LyP (50%), 4/6 PC-ALCL (67%) and 9/12 MF-LCT (75%). Two of 12 PLEVA (17%), 1 of 12 ABR (8%) and 2 of 8 LR (25%) had lymphocytes (< 25%) with diffuse cytoplasmic staining. Dermal dendritic cells stained strongly for clusterin. High background staining occurred in some cases. CONCLUSION: Clusterin immunostaining does not reliably distinguish between LyP, PC-ALCL or MF-LCT, but could distinguish LyP from its reactive histologic simulants.

Comparison of CD23 staining patterns in Merkel cell carcinoma and non-cutaneous small cell carcinoma.

BACKGROUND: During our daily practice, we observed that cluster designation 23 (CD23) (clone BU38) labels Merkel cells in normal skin. In this study, we examined the expression of CD23 in Merkel cell carcinoma (MCC) and assessed its usefulness in distinguishing MCC from non-cutaneous small cell carcinoma (SMCC). METHODS: Immunohistochemical staining of CD23 was performed on a total of 33 MCCs, 22 SMCCs and 5 carcinoid tumors. RESULTS: CD23 reactivity was present in 32 of 33 (97%) MCCs, 18 of 22 (82%) SMCCs and 5 of 5 (100%) carcinoid tumors. In MCC, 19 cases (59%) showed a predominance of perinuclear dot-like staining similar to cytokeratin 20, 3 (9%) showed mostly cytoplasmic staining and 10 (31%) displayed a combination of perinuclear dot-like and cytoplasmic staining. In contrast, all CD23-positive SMCCs and carcinoid tumors showed a diffuse cytoplasmic staining. There was a significant difference in the CD23 staining patterns between MCC and SMCC (p < 0.0001). CONCLUSION: CD23 is expressed in the majority of MCC, SMCC and carcinoid tumor irrespective of clinical outcome. The distinct punctate CD23 staining for MCC may be helpful in differentiating it from SMCC. To our knowledge, this is the first study to show the expression of CD23 in neuroendocrine tumors.

Diagnostic value of CD163 in cutaneous spindle cell lesions.

BACKGROUND: The histologic diagnosis of atypical fibroxanthoma (AFX) can sometimes be challenging. No specific marker exists to confirm the diagnosis other than excluding other entities. CD163 has been shown to have great specificity for tumors of monocyte/histiocyte lineage. In this study, we evaluated the diagnostic utility of CD163 in diagnosing AFX and in identifying skin lesions with histiocytic/dendritic derivation. METHODS: A total of 157 cases, including 14 AFXs, 5 spindle cell squamous cell carcinomas (SCCs), and 7 spindle cell/desmoplastic melanomas, along with other cutaneous spindle cell and histiocytic/fibrohistiocytic lesions, were stained with CD163. RESULTS: CD163 was expressed in 11 of 14 (79%) AFXs, with moderate to strong intensity. No staining was observed in cases of spindle cell SCC (0/5) and dermatofibrosarcoma protuberans (0/10). Rare spindle cell/desmoplastic melanomas (2/7) and cutaneous leiomyosarcomas (1/5) demonstrated positive staining. CD163 reactivity was seen in 24 of 29 of benign fibrous histiocytomas (BFHs), including 8 of 8 cellular fibrous histiocytomas and 6 of 9 epithelioid cell histiocytomas. The majority of cutaneous histiocytic lesions, including juvenile xanthogranuloma, Langerhans cell histiocytosis and Rosai-Dorfman disease, were positive for CD163. CONCLUSION: CD163 is a useful adjunct in distinguishing AFX from other malignant cutaneous spindle cell tumors and offers improved specificity in identifying cutaneous histiocytic/dendritic lesions.