Analysis of microphthalmia transcription factor expression in normal tissues and tumors, and comparison of its expression with S-100 protein, gp100, and tyrosinase in desmoplastic malignant melanoma

An Update and Review of Clinical Outcomes Using Immunohistochemical Stains in Mohs Micrographic Surgery for Melanoma

BACKGROUND

Mohs micrographic surgery (MMS) provides optimal margin control through complete peripheral and deep margin assessment. The treatment of melanoma using MMS has historically been limited by difficulty in interpreting melanocytes using frozen sections. Immunohistochemical (IHC) staining, a technique whereby chromogen-tagged antibodies are used to detect antigens of interest, has revolutionized the surgical treatment of melanoma.

OBJECTIVES

This article provides an update and literature review of current IHC stains used in MMS for melanoma, their sensitivities and specificities, and clinical outcomes.

MATERIALS AND METHODS

A PubMed search was performed using keywords including "immunohistochemistry," "staining," and "Mohs surgery." Articles related to the use of IHC staining for the treatment of melanoma with MMS were included.

RESULTS

Six IHC stains met the criteria for the review including melanoma antigen recognized by T cells (MART-1), SRY-related HMG-box (SOX10), microphthalmia-associated transcription factor, HMB-45, MEL-5, S-100, and preferentially expressed antigen in melanoma.

CONCLUSION

The adaptation of IHC methods to frozen sections has enabled MMS to become a preferred treatment option for melanoma in special-site areas. Future studies are needed to standardize IHC techniques and to define best practices when using frozen section in the treatment of melanoma.

Pitfalls in Cutaneous Melanoma Diagnosis and the Need for New Reliable Markers

Cutaneous melanoma is one of the most aggressive forms of skin cancer, with the development of advanced stage disease resulting in a high rate of patient mortality. Accurate diagnosis of melanoma at an early stage is essential to improve patient outcomes, as this enables treatment before the cancer has metastasised. Histopathologic analysis is the current gold standard for melanoma diagnosis, but this can be subjective due to discordance in interpreting the morphological heterogeneity in melanoma and other skin lesions. Immunohistochemistry (IHC) is sometimes employed as an adjunct to conventional histology, but it remains occasionally difficult to distinguish some benign melanocytic lesions and melanoma. Importantly, the complex morphology and lack of specific biomarkers that identify key elements of melanoma pathogenesis can make an accurate confirmation of diagnosis challenging. We review the diagnostic constraints of melanoma heterogeneity and discuss issues with interpreting routine histology and problems with current melanoma markers. Innovative approaches are required to find effective biomarkers to enhance patient management.

Cutaneous Melanomas: A Single Center Experience on the Usage of Immunohistochemistry Applied for the Diagnosis

Cutaneous melanoma (cM) is the deadliest of all primary skin cancers. Its prognosis is strongly influenced by the stage at diagnosis, with early stages having a good prognosis and being potentially treatable with surgery alone; advanced stages display a much worse prognosis, with a high rate of recurrence and metastasis. For this reason, the accurate and early diagnosis of cM is crucial-misdiagnosis may have extremely dangerous consequences for the patient and drastically reduce their chances of survival. Although the histological exam remains the "gold standard" for the diagnosis of cM, a continuously increasing number of immunohistochemical markers that could help in diagnosis, prognostic characterization, and appropriate therapeutical choices are identified every day, with some of them becoming part of routine practice. This review aims to discuss and summarize all the data related to the immunohistochemical analyses that are potentially useful for the diagnosis of cM, thus rendering it easier to appropriately applicate to routine practice. We will discuss these topics, as well as the role of these molecules in the biology of cM and potential impact on diagnosis and treatment, integrating the literature data with the experience of our surgical pathology department.

PRAME immunohistochemistry as an adjunct for diagnosis and histological margin assessment in lentigo maligna

AIMS

Lentigo maligna (LM), the most common type of melanoma in situ, is a diagnostically challenging lesion for pathologists due to abundant background melanocytic hyperplasia in sun-damaged skin. Currently, no laboratory methods reliably distinguish benign from malignant melanocytes. However, preferentially expressed antigen in melanoma (PRAME) has shown promise in this regard, and could potentially be applied to diagnosis and margin assessment in difficult cases of LM.

METHODS AND RESULTS

Ninety-six cases with a diagnosis of LM (n = 77) or no residual LM (n = 19) following initial biopsy were identified and stained with an antibody directed towards PRAME. Immunohistochemistry (IHC) was scored as positive or negative, and measurement of histological margins by PRAME was performed and compared to the measurement of histological margins using conventional methods [haematoxylin and eosin (H&E) and/or sex-determining region Y-box 10 (SOX10) and/or Melan-A]. Of cases with LM, 93.5% (72 of 77) were PRAME+ and 94.7% (18 of 19) of cases with no residual LM were PRAME- . Of the 35 cases with no margin involvement by PRAME or conventional assessment, 14 cases (40.0%) had no difference in measurement, 17 (48.6%) had a difference of 1 mm or less and four (11.4%) differed by between 1 and 3.5 mm. There was a high correlation between margin assessment methods (r = 0.97, P < 0.0001).

CONCLUSIONS

PRAME IHC is a sensitive (93.5%) and specific (94.7%) method for diagnosing LM on biopsy and excision, and measurement of histological margins by PRAME shows a high correlation with conventional methods for margin assessment. Furthermore, the nuclear expression of PRAME makes it a good target for use in dual-colour IHC stains.

Melanoma Biomarkers and Their Potential Application for In Vivo Diagnostic Imaging Modalities

Melanoma is the deadliest form of skin cancer and remains a diagnostic challenge in the dermatology clinic. Several non-invasive imaging techniques have been developed to identify melanoma. The signal source in each of these modalities is based on the alteration of physical characteristics of the tissue from healthy/benign to melanoma. However, as these characteristics are not always sufficiently specific, the current imaging techniques are not adequate for use in the clinical setting. A more robust way of melanoma diagnosis is to "stain" or selectively target the suspect tissue with a melanoma biomarker attached to a contrast enhancer of one imaging modality. Here, we categorize and review known melanoma diagnostic biomarkers with the goal of guiding skin imaging experts to design an appropriate diagnostic tool for differentiating between melanoma and benign lesions with a high specificity and sensitivity.

An Algorithmic Immunohistochemical Approach to Define Tumor Type and Assign Site of Origin

Immunohistochemistry represents an indispensable complement to an epidemiology and morphology-driven approach to tumor diagnosis and site of origin assignment. This review reflects the state of my current practice, based on 15-years' experience in Pathology and a deep-dive into the literature, always striving to be better equipped to answer the age old questions, "What is it, and where is it from?" The tables and figures in this manuscript are the ones I "pull up on the computer" when I am teaching at the microscope and turn to myself when I am (frequently) stuck. This field is so exciting because I firmly believe that, through the application of next-generation immunohistochemistry, we can provide better answers than ever before. Specific topics covered in this review include (1) broad tumor classification and associated screening markers; (2) the role of cancer epidemiology in determining pretest probability; (3) broad-spectrum epithelial markers; (4) noncanonical expression of broad tumor class screening markers; (5) a morphologic pattern-based approach to poorly to undifferentiated malignant neoplasms; (6) a morphologic and immunohistochemical approach to define 4 main carcinoma types; (7) CK7/CK20 coordinate expression; (8) added value of semiquantitative immunohistochemical stain assessment; algorithmic immunohistochemical approaches to (9) "garden variety" adenocarcinomas presenting in the liver, (10) large polygonal cell adenocarcinomas, (11) the distinction of primary surface ovarian epithelial tumors with mucinous features from metastasis, (12) tumors presenting at alternative anatomic sites, (13) squamous cell carcinoma versus urothelial carcinoma, and neuroendocrine neoplasms, including (14) the distinction of pheochromocytoma/paraganglioma from well-differentiated neuroendocrine tumor, site of origin assignment in (15) well-differentiated neuroendocrine tumor and (16) poorly differentiated neuroendocrine carcinoma, and (17) the distinction of well-differentiated neuroendocrine tumor G3 from poorly differentiated neuroendocrine carcinoma; it concludes with (18) a discussion of diagnostic considerations in the broad-spectrum keratin/CD45/S-100-"triple-negative" neoplasm.

Meningioma-like Tumor of the Skin Revisited: A Distinct CD34+ Dermal Tumor With an Expanded Histologic Spectrum

The term meningioma-like tumor of the skin (MLTS) was coined in 1993 to designate a particular whorled spindle cell superficial cutaneous tumor. No additional confirmed cases of this entity have been reported to date. Some authors have speculated that these cases might be cellular neurothekeomas. In order to delineate the histologic spectrum and the immunophenotype of this unusual tumor, we studied 5 cases, 2 previously unreported and the 3 original cases. The immunohistochemical findings of case 5, however, were limited to those from the original study. Clinically, the tumor presented as a reddish papule, plaque, or nodule, located in the extremities or trunk. The patient often referred to a recent growth of a longstanding lesion. Histologically, the characteristic whorled spindle and stellate dendritic cell population, commonly in a perivascular arrangement, and variable myxoid component, were consistently found in all cases. A prominent microvasculature was also a constant finding. The presence of large deciduoid cells was conspicuous in one case. A reticular pattern of multivacuolated cells giving a chordoma-like appearance was evident in another case. Tumor cells were diffusely positive for CD34 in all 4 cases studied, and negative for S-100, EMA, NKI-C3, CD68, and smooth muscle markers. No complete loss of retinoblastoma protein was found. No brachyury immunostaining was found in the case with chordoid features. No EWSR1 or NAB2-STAT6 gene fusions were found. From these findings, we demonstrate that MLTS is a distinct CD34 spindle cell benign dermal tumor, unrelated to cellular neurothekeoma, and exhibiting myxoid, deciduoid, or chordoma-like features.

Molecular phenotyping and image-guided surgical treatment of melanoma using spectrally distinct ultrasmall core-shell silica nanoparticles

Accurate detection and quantification of metastases in regional lymph nodes remain a vital prognostic predictor for cancer staging and clinical outcomes. As intratumoral heterogeneity poses a major hurdle to effective treatment planning, more reliable image-guided, cancer-targeted optical multiplexing tools are critically needed in the operative suite. For sentinel lymph node mapping indications, accurately interrogating distinct molecular signatures on cancer cells in vivo with differential levels of sensitivity and specificity remains largely unexplored. To address these challenges and demonstrate sensitivity to detecting micrometastases, we developed batches of spectrally distinct 6-nm near-infrared fluorescent core-shell silica nanoparticles, each batch surface-functionalized with different melanoma targeting ligands. Along with PET imaging, particles accurately detected and molecularly phenotyped cancerous nodes in a spontaneous melanoma miniswine model using image-guided multiplexing tools. Information afforded from these tools offers the potential to not only improve the accuracy of targeted disease removal and patient safety, but to transform surgical decision-making for oncological patients.

Distinguishing Neurofibroma From Desmoplastic Melanoma: The Value of p53

Distinguishing desmoplastic melanomas (DMs) from neurofibromas (NFs) can be histologically challenging in some cases. To date, a reliable marker to differentiate the 2 entities has remained elusive. S100 subtyping and CD34 fingerprinting have been proposed, but controversy remains as to their reliability. Missense mutations in TP53 are often found in DMs, resulting in a dominant negative effect and paradoxical accumulation of the tumor suppressor protein p53. We hypothesized that p53 may be expressed differentially in DMs, making it a valuable tool in differentiating DMs from NFs. Using immunohistochemistry, we compared p53 protein expression in 20 DMs and 20 NFs retrieved from our tissue archives and stained with p53 antibody (Monoclonal, DO-7). Patients with DM included 18 men and 2 women (age, 36 to 95 y; mean, 70.5 y; median, 70 y). Fifteen (15/20) tumors occurred in head and neck area; 2 (2/20) on the trunk; and 3 (3/20) on the extremities. Patients with NF included 12 men and 8 women (age, 47 to 85 y; mean, 65.2 y; median, 69.5 y). Eleven (11/20) tumors occurred on the trunk, 6 (6/20) on the extremities, and 3 (3/20) on the head and neck area. A total of 19/20 (95%) DMs were positive for p53. DM Histo-scores ranged from 0 to 300 (mean, 203; median, 260). Nuclear accumulation of p53 was seen in all 19 positive DMs. None of the 20 NFs were positive for p53 (2-tailed t test P-value <0.0001). Detection of p53 by immunohistochemistry can help to distinguish DMs from NFs.

Evaluation of eight melanocytic and neural crest-associated markers in a well-characterised series of 124 malignant peripheral nerve sheath tumours (MPNST): useful to distinguish MPNST from melanoma?

AIMS

The diagnosis of malignant peripheral nerve sheath tumour (MPNST) may be challenging, especially in the sporadic setting. Owing to the lack of specific histological criteria, immunohistochemical and molecular diagnostic markers, several differential diagnoses must be considered, especially melanoma. Indeed, although S100 protein usually stains melanoma, other melanocytic markers are often negative, especially in spindle cell/desmoplastic types. This pattern of immunoreactivity resembles that of some nerve-derived tumours such as MPNST. Owing to their different clinical behaviours and therapeutic implications, accurate identification of these two different tumours is crucial.

METHODS AND RESULTS

S100, SOX10, KBA62, MITF, HMB45, Melan-A, tyrosinase PNL2 and BRAF-V600E immunostaining was performed in a pathologically and genetically well-characterised cohort of primary MPNST (n = 124), including 66 (53%) NF1-associated tumours. Sox10 and KBA62 expression were found, respectively, in 102 (84%) and in 101 (83%) MPNST, whereas S100 was expressed in 64 cases (52%). We observed an increased loss of S100 with increasing histological grade (P = 0.0052). We found Melan-A expression in 14% (n = 17) of all MPNST, occurring in 82% (n = 14) of cases in an NF1 context. Six per cent (n = 8) of MPNST showed tyrosinase positivity, including seven (87%) NF1-associated. MITF expression was found in 10 (8%) MPNST. None expressed PNL2, HMB45 or BRAF-V600E.

CONCLUSION

MPNST (in NF1 and a sporadic setting) can quite often be positive for Melan-A, tyrosinase and MITF. Pathologists should be cognisant of these exceptions to prevent confusion with melanoma.

Microphthalmia-associated transcription factor (MiTF): Promiscuous staining patterns in fibrohistiocytic lesions is a potential pitfall

Microphthalmia-associated transcription factor (MiTF) is used as a marker of melanocytic differentiation. However, MiTF immunoexpression has also been observed in histiocytes, macrophages, smooth muscle cells and fibroblasts, which raise the concern of fibrohistiocytic (FH) lesions being misdiagnosed as melanoma based on MiTF immunoreactivity. MiTF has been known to be positive in FH tumors, but this is the first study evaluating ninety-three fibrohistiocytic neoplasms to understand and delineate the staining pattern of MiTF in these tumors. Ninety-three cases of FH, 30 cases of melanocytic lesions, and 20 miscellaneous cases were studied. The FH cases included benign fibrous histiocytoma (BFH, n = 29), angiofibroma (AF, n = 11), fibromatosis (FM, n = 14), keloid (KE, n = 10), atypical fibroxanthoma (AFX, n = 7), dermal scar (DS, n = 9), dermatofibrosarcoma protuberans (DFSP, n = 12), and pigmented DFSP (Bednar tumor, n = 1). Benign fibrous histiocytoma were sub-categorized into dermatofibroma (n = 15) and epithelioid fibrous histiocytoma (n = 14). The melanocytic lesions included desmoplastic melanoma (DM, n = 8), melanoma in-situ (MIS, n = 5), re-excision-free of melanoma (RFM, n = 10), blue nevus (BN, n = 5), and spitz nevus (SN, n = 3). The miscellaneous category included osteosarcoma (OS, n = 3), pigmented basal cell carcinoma (PBCC, n = 5), spindle cell squamous cell carcinoma (SCA, n = 2), and giant cell tumor of tendon sheath (GCTTS, n = 10). All BFH, AF, AFX, KE, and DS cases showed a positive MiTF staining of variable extent and intensity. MiTF positivity was observed in 86% (n = 12) cases of FM and 17% (n = 2) cases of DFSP. Amongst the miscellaneous category, all cases of PBCC and GCTTS and 50% (n = 1) cases of SCA were immunoreactive for MiTF. All melanocytic lesions were positive for MiTF. None of the OS and pigmented DFSP showed positive labeling. Because of the promiscuity of MiTF labeling, awareness of its pattern in FH proliferations may avoid potential pitfalls in the diagnosis of spindle cell lesions.

NF1 Mutations Are Common in Desmoplastic Melanoma

Desmoplastic melanoma (DM) is a rare variant of melanoma with distinct clinical, histopathologic, and immunohistochemical features. Clinically, DM differs from conventional melanoma by a higher propensity for local recurrence and less frequent metastatic spread to regional lymph nodes. In its pure form, DM has a distinct appearance displaying a low density of fusiform melanocytes in a collagen-rich matrix. Whereas a number of mutations have been identified in primary melanoma, including BRAF, NRAS, GNAQ, GNA11, and KIT, and the occurrence of these mutations has been found to correlate to some extent with the histopathologic features, anatomic site, and/or mode of sun exposure, no distinct set of mutations has so far been reported for DM. To study the potential association of neurofibromin (NF1) mutations with DM, we examined 15 desmoplastic and 20 non-DMs by next-generation sequencing. Mutations of the NF1 gene were found in 14 of 15 (93%) DMs and 4 of 20 (20%) non-DMs. The high frequency of NF1 mutations in DMs suggests an important role for NF1 in the biology of this type of melanoma.

An update on the application of newly described immunohistochemical markers in soft tissue pathology

CONTEXT

During the last 5 to 10 years, significant progress has been made in the molecular characterization of soft tissue tumors, predominantly with the identification of recurrent translocations or amplification of certain genes in different tumor types. Alongside this, translational efforts have identified many novel and diagnostically useful immunohistochemical markers for many of these tumor types.

OBJECTIVE

This article reviews a select group of recently described immunohistochemical markers of particular use in the evaluation of mesenchymal neoplasms; the underlying biology of the protein product, practical utility, and limitations of each marker are discussed in detail.

DATA SOURCES

Literature review, authors' research data, and personal practice experience serve as sources.

CONCLUSIONS

There are many diagnostically useful immunohistochemical markers to help confirm the diagnosis of many different soft tissue tumor types, some of which have reduced the need for additional, and more costly, studies, such as fluorescence in situ hybridization. However, no one marker is 100% specific for a given tumor, and knowledge of potential pitfalls and overlap in patterns of staining among other tumor types is crucial to ensure the appropriate application of these markers in clinical practice.

Emerging clinical applications of selected biomarkers in melanoma

Melanoma is a lethal skin disease with a mostly predictable clinical course according to a known constellation of clinical and pathologic features. The distinction of melanoma from benign melanocytic nevus is typically unequivocol; however, there is a subset of tumors known for its diagnostic challenges, development of late metastases, and difficulties in treatment. Several melanocytic tissue biomarkers are available that can facilitate the histopathologic interpretation of melanoma as well as provide insight into the biologic potential and mutational status of this disease. This review describes the clinical application of some of these established and emerging tissue biomarkers available to assess melanocytic differentiation, vascular invasion, mitotic capacity, and mutation status. The selected tissue biomarkers in this review include MiTF, Sox10, D2-40, PHH3, H3KT (anti-H3K79me3T80ph), anti-BRAFV600E, and anti-BAP-1.

Value of melanocytic-associated immunohistochemical markers in the diagnosis of malignant melanoma: a review and update

Since the identification of S100 protein as an immunohistochemical marker that could be useful in the diagnosis of melanoma in the early 1980s, a large number of other melanocytic-associated markers that could potentially be used to assist in the differential diagnosis of these tumors have also been investigated. A great variation exists, however, among these markers, not only in their expression in some subtypes of melanoma, particularly desmoplastic melanoma, but also in their specificity because some of them can also be expressed in nonmelanocytic neoplasms, including various types of soft tissue tumors and carcinomas. This article reviews the information that is currently available on the practical value of some of the markers that have more often been recommended for assisting in the diagnosis of melanomas, including those that have only recently become available.

Desmoplastic melanoma: a review

Desmoplastic melanoma (DM) is a variant of spindle cell melanoma typically found on chronically sun-damaged skin of older individuals. Early diagnosis can be challenging because it is often amelanotic and has a predominantly dermal component. DM can be difficult to diagnose not only clinically but also histologically, and can be mistaken for a variety of benign and malignant nonmelanocytic spindle cell tumors when viewed on prepared histopathology slides. Pathologists have observed that DMs can manifest significant variation with respect to the extent of intratumoral cellularity, fibrosis, and/or perineural invasion. Furthermore, some tumors present with a pure desmoplastic invasive component (>90%) while other tumors display mixed features of DM and nondesmoplastic melanoma. This has led to the separation of DM into 2 histologic subtypes, pure and mixed. With a focus on the distinction between pure and mixed DM, this review will detail what is currently known about the diagnostic features of DM, discuss risk and prognostic factors, and examine the current literature on disease progression and management.

Sox10 is expressed in primary melanocytic neoplasms of various histologies but not in fibrohistiocytic proliferations and histiocytoses

BACKGROUND

Sox10 is a transcription factor associated with neural crest development. Its expression has been reported in melanocytes and peripheral nerve sheath cells and their associated tumors.

OBJECTIVE

To assess Sox10 sensitivity in benign and malignant melanocytic neoplasms of various histologic subtypes and to discern the specificity of Sox10 in distinguishing between melanocytic neoplasms and fibrohistiocytic and histiocytic mimickers.

METHODS

Sox10 expression was examined by immunohistochemistry in 145 cases of formalin-fixed paraffin-embedded tissue, including benign and malignant melanocytic lesions of various histologies and stages (n = 83), fibrohistiocytic and histiocytic lesions (n = 33), and peripheral nerve sheath tumors (n = 19), among others (n = 10).

RESULTS

Immunoreactivity with Sox10 was observed in 100% (83/83) of benign and malignant melanocytic lesions of various subtypes, as well as in 100% (19/19) of benign and malignant peripheral nerve sheath lesions. Among the fibrohistiocytic proliferations and histiocytoses examined, Sox10 was negative in all cases (0/33). Sox10 expression did not vary by histologic subtype in nevi or melanoma; however, both the percentage of tumor nuclei demonstrating Sox10 expression and the intensity of expression were inversely correlated with malignant potential (nevi, melanoma in situ, invasive and metastatic melanoma) (P < .001, P = .016, respectively). Malignant peripheral nerve sheath tumors also showed decreased mean Sox10 expression and decreased intensity of expression when compared with benign counterparts (P < .001, P = .021, respectively).

LIMITATIONS

This is a retrospective study with 145 cases included.

CONCLUSIONS

Sox10 is a highly sensitive marker for melanocytic proliferations and may be useful diagnostically when the differential diagnosis includes fibrohistiocytic and histiocytic proliferations demonstrating S100 expression.

Mohs surgery for melanoma: rationale, advances and possibilities

Mohs surgery (MS) is an effective technique for the removal of a variety of cutaneous neoplasms by virtue of its thorough assessment of margins. It has yet to become widely accepted for melanoma because recognizing melanocytes histologically in frozen section can be problematic. Recently, 'rapid' methods of immunohistochemistry have been developed that resolve this issue by staining the melanocytes in frozen section. In addition, some of the immunohistochemistry protocols that previously required up to 1 h now take 19 min or less. These technological enhancements for MS have removed some of the obstacles towards the acceptance of MS as a legitimate option for removal of melanomas, especially poorly demarcated lesions and lesions from the head and neck, the distal extremities and the genitalia. Experience thus far with MS for melanoma has shown lower recurrence rates and improved disease-specific survival compared with historical controls for standard excision, while at the same time minimizing the sacrifice of normal tissue.

Tissue microarray analysis of ezrin, KBA.62, CD166, nestin, and p-Akt in melanoma versus banal and atypical nevi, and nonmelanocytic lesions

Multiple melanocytic markers are useful for differentiating between melanoma and nonmelanocytic lesions but generally do not distinguish melanoma from nevi and atypical melanocytic lesions. We sought to determine if several immunohistochemical markers recently described in the literature, including ezrin, KBA.62, p-Akt, CD166, and nestin, may be helpful in distinguishing these lesions. One hundred ten tissue microarray samples were scored for nestin and CD166 and 220 samples for ezrin, KBA.62, and p-Akt. We found that putative stem cell markers nestin and CD166 were both expressed in most melanomas (86% and 65% of samples, respectively), including desmoplastic melanoma, but were also expressed at similar levels in nevi (79% and 74%, respectively). In addition, these markers were not specific for melanocytic lesions. Ezrin was also expressed in both nevi and melanoma (81% each), including desmoplastic melanoma (75%), and in neural tumors. KBA.62 stained more cases of nevi versus melanoma (93% and 65%, respectively) and was positive in 53% of desmoplastic melanoma. However, it was also positive in several nonmelanocytic tumors. P-Akt expression was generally weak but was increased in nevi (75%) versus melanoma (43%), and was lost in desmoplastic melanomas (5%). Overall, only KBA.62 and p-Akt expression differed between melanoma and nevi, and none of these markers were completely specific for melanocytic tumors versus nonmelanocytic lesions.

Desmoplastic melanoma

Desmoplastic melanoma (DM) is a variant of spindle cell melanoma characterized by the presence of abundant fibrous matrix. It is typically found in the head and neck region on chronically sun-damaged skin of older individuals. Early detection is uncommon, because its clinical features are not distinctive. DM is prone to misdiagnosis not only clinically but also histologically. It may simulate a sclerosing melanocytic nevus and various benign and malignant nonmelanocytic lesions. Among melanomas said to be desmoplastic by various pathologists there is significant variation with regard to the extent of intratumoral fibrosis. It may be prominent throughout the entire tumor (pure DM) or represent a portion of an otherwise nondesmoplastic melanoma (combined DM). Immunophenotypically, DM are usually strongly and homogeneously positive for S-100 protein, but are often negative or only focally positive for melanocyte differentiation antigens. DM differs from conventional melanoma in its clinical course. It is associated with a higher tendency for local recurrence, but metastases to regional lymph nodes are less common.

Primary retroperitoneal malignant melanoma: A case report

Primary malignant melanoma occurring at an extra cutaneous site is rare. A case of primary malignant melanoma located in the retroperitoneum of an 18-year-old female is presented in this study. Histopathological examination of the tissue biopsies at laparotomy with immunohistochemical stains confirmed a diagnosis of malignant melanoma. Further extensive clinical and radiological investigations proved the retroperitoneum to be the primary site.

Biology and clinical relevance of the micropthalmia family of transcription factors in human cancer

Members of the micropthalmia (MiT) family of transcription factors (MITF, TFE3, TFEB, and TFEC) are physiologic regulators of cell growth, differentiation, and survival in several tissue types. Because their dysregulation can lead to melanoma, renal cell carcinoma, and some sarcomas, understanding why these genes are co-opted in carcinogenesis may be of general utility. Here we describe the structure of the MiT family of proteins, the ways in which they are aberrantly activated, and the molecular mechanisms by which they promote oncogenesis. We discuss how meaningful understanding of these mechanisms can be used to elucidate the oncogenic process. Because the expression of these proteins is essential for initiating and maintaining the oncogenic state in some cancer types, we propose ways that they can be exploited to prevent, diagnose, and rationally treat these malignancies.

Differential LEF1 and TCF4 expression is involved in melanoma cell phenotype switching

Recent observations suggest that melanoma cells drive disease progression by switching back and forth between phenotypic states of proliferation and invasion. Phenotype switching has been linked to changes in Wnt signalling, and we therefore looked for cell phenotype-specific differences in the levels and activity of β-catenin and its LEF/TCF co-factors. We found that while cytosolic β-catenin distribution is phenotype-specific (membrane-associated in proliferative cells and cytosolic in invasive cells), its nuclear distribution and activity is not. Instead, the expression patterns of two β-catenin co-factors, LEF1 and TCF4, are both phenotype-specific and inversely correlated. LEF1 is preferentially expressed by differentiated/proliferative phenotype cells and TCF4 by dedifferentiated/invasive phenotype cells. Knock-down experiments confirmed that these co-factors are important for the phenotype-specific expression of M-MITF, WNT5A and other genes and that LEF1 suppresses TCF4 expression independently of β-catenin. Our data show that melanoma cell phenotype switching behaviour is regulated by differential LEF1/TCF4 activity.

Distinguishing neurofibroma from desmoplastic melanoma: the value of the CD34 fingerprint

We have observed 'fingerprint' immunopositivity in association with perineurioma and neurofibroma. A fingerprint consists of delicate, elongated areas of positive labeling that fall between collagen bundles, thereby creating a whorled configuration that is reminiscent of a human fingerprint. At present, the differential diagnosis between early desmoplastic melanoma and neurofibroma remains challenging in a subset of cases because of overlapping histopathological and immunohistochemical features. To assess whether fingerprint CD34 reactivity could be contributory in this context, we stained 50 desmoplastic melanomas and 50 neurofibromas with CD34. Fingerprint CD34 labeling was present in greater than 30% of the proliferation in 96% (n = 48) of neurofibromas and in only 4% (n = 2) of desmoplastic melanomas. Over two-thirds of the neurofibromas exhibited a CD34 fingerprint involving more than 60% of their surface area. In the two cases of desmoplastic melanoma that showed CD34 fingerprint positivity, the staining was patchy and involved less than 60% of the tumor. In partially staining neurofibromas, areas without a CD34 fingerprint tended to occur in central lobular areas. We conclude that CD34 fingerprint immunoreactivity is useful in distinguishing neurofibroma from early desmoplastic melanoma, especially if the fingerprint involves more than 60% of a tumor's cross-sectional area.

P75 nerve growth factor receptor staining is superior to S100 in identifying spindle cell and desmoplastic melanoma

BACKGROUND

Spindle cell melanoma (SCM) including desmoplastic melanoma (DM) is a rare variant of malignant melanoma that may present diagnostic difficulties particularly when staining with S100 is negative, weak, focal, or a combination of these. Conventional melanocytic markers in SCM are usually negative.

OBJECTIVE

We sought to compare the staining of p75 nerve growth factor receptor (NGF-R) and S100 in SCMs.

METHODS

We evaluated the staining of p75 NGF-R and S100 in 13 cases of SCMs: 3 SCMs without desmoplasia, 5 pure DMs, and 5 combined DMs with a conventional component.

RESULTS

Staining with p75 NGF-R was positive in 13 of 13 (100%) cases of SCMs. In 3 cases the intensity of staining and the percentage of cells staining with this marker were greater than those with S100. One case of SCM was negative for S100 but demonstrated strong expression of p75 NGF-R. One case was focally and weakly positive with S100 but expressed strong positive staining with p75 NGF-R. Absence of staining with p75 NGF-R was noted in the conventional round cell component of two of 5 (40%) combined DMs whereas the same areas were strongly positive for human melanoma black (HMB)-45 and Melan-A. In 5 of 5 (100%) cases of combined DMs the desmoplastic component stained positive with p75 NGF-R, demonstrating an inverse relationship with the staining of conventional melanocytic markers.

LIMITATIONS

Small study size was a limitation.

CONCLUSION

p75 NGF-R exhibits superior staining characteristics and greater sensitivity in identifying SCM and DMs than S100. P75 NGF-R may be a useful diagnostic and ancillary stain in addition to S100.

Use of immunohistochemistry in the diagnosis of melanocytic lesions: applications and pitfalls

The accurate diagnosis of melanocytic lesions is essential for the adequate clinical management of the patients. Besides the histopathologic examination, immunohistochemical studies are often used as an adjunct in distinguishing melanocytic lesions from tumors with different origin or between benign and malignant melanocytic lesions. In the first part of this article, we analyze data on currently used immunohistochemical markers, with special emphasis on their applicability to clinical practice, and underline their potential pitfalls. The pathogenesis of malignant transformation of melanocytes is not completely understood. Recent studies report that various melanoma progression markers are preferentially expressed in benign or malignant melanocytic lesions or show different expression in subsequent stages of tumor development. Furthermore, in recent years, emerging genetic studies suggest that there are distinctive patterns of chromosomal aberrations in different subtypes of melanoma that can be altered by newly developed targeted therapies. In the second part of our article, we will discuss the most significant progression markers in melanoma that can be detected by immunohistochemistry and their potential usefulness for diagnosis, prognosis, staging or as therapeutic targets.