Xanthogranulomas with inconspicuous foam cells and giant cells mimicking malignant melanoma: a clinical, histologic, and immunohistochemical study of three cases

Histiocytoid melanoma: Diagnostic pitfall and mimicker of non-Langerhans cell histiocytoses including reticulohistiocytoma

Melanoma and benign histiocytic proliferations can sometimes show considerable clinical and histopathologic overlap. Recently, cases of melanomas resembling xanthogranuloma and Rosai-Dorfman disease have been reported, and herein we report a case of melanoma closely mimicking reticulohistiocytoma. An 84-year-old man presented with a 1 cm purple-red nodule on his arm concerning for squamous cell carcinoma. While the biopsy findings resembled reticulohistiocytoma, the clinical context and regression changes at the lesion perimeter raised stronger concern for melanoma, which was confirmed with immunohistochemistry. We review prior rare reports of melanomas resembling non-Langerhans cell histiocytic proliferations and summarize helpful clinical and histopathologic clues to avoid a diagnostic pitfall when confronted with this unusual quandary.

Metastatic melanoma with balloon/histiocytoid cytomorphology after treatment with immunotherapy: A histologic mimic and diagnostic pitfall

Epithelioid cells with foamy cytoplasm (histiocytoid features) are typical histopathologic findings among benign and malignant histiocytic neoplasms such as xanthoma and atypical fibroxanthoma. However, these changes are unusual in melanoma, which is typically composed of nested and variably pigmented atypical epithelioid cells. Here, we report a patient with metastatic melanoma in lymph nodes presenting with prominent balloon cell/histiocytoid features expressing melanocytic markers, after treatment with nivolumab. This report suggests that the spectrum of neoplasms with histiocytoid features should be expanded to include melanoma, a pattern that, to the best of our knowledge, is uncommon, especially in the setting of post-neoadjuvant therapy.

Diagnostic immunohistochemistry through Rosai-coloured glasses

Over the past three decades, Immunohistochemistry has materially changed the practice of diagnostic surgical pathology. Foundational observations in this field were critical to a reasoned assessment of both the risks and opportunities that immunohistochemistry afforded the surgical pathologist, and our current practice draws heavily on those early assessments. As we collectively look to and acknowledge those who recognized the value of this technique and who helped guide its development as a companion to (not a replacement for) histomorphologic evaluation, we are drawn to those whose mastery of detail and ability to draw common patterns from seemingly unrelated phenomena helped define the diagnostic power of immunohistochemistry. The focus of this review is on one individual, Dr. Juan Rosai, whose contributions transcend the simple linkage of molecular observations to morphology, recognizing novel patterns in both form and color (the latter often the lovely shades of diaminobenzidine), seemingly viewing our diagnostic world at times through an entirely different lens. By looking at Dr. Rosai's early work in this field, reviewing a selection of his seminal observations, particularly in the Immunohistochemistry of thyroid and thymic neoplasia, revisiting how his special insight is often guided by the work of the early masters of morphology, and how his mentorship of others has helped shaped academic surgical pathology practice, perhaps we can get a glimpse through that lens.

Nonlipidized juvenile xanthogranuloma: an unusual variant with a potential diagnostic pitfall

Juvenile xanthogranuloma (JXG) is a histiocytic inflammatory disorder that can present different histologic patterns. Classic JXG consists of sheets of foamy histiocytes and numerous multinucleated Touton giant cells. Nonlipidized JXG (NJXG) is one of the unusual variants of JXG, consisting of a diffuse monomorphic infiltrate of mononuclear histiocytes, suggesting an aggressive or malignant tumor due the high mitotic index. However, NJXG behaves clinically as classic JXG. We present an unusual case of a 6-year-old boy who presented an exophytic ulcerated nodule on the lower lip diagnosed as NJXG. The boy is currently well without recurrence three years after surgical excision.

CD163 expression is present in cutaneous histiocytomas but not in atypical fibroxanthomas

CD163, a hemoglobin scavenger receptor, is expressed in monocytes and macrophages. Recent work has shown that this marker is specific for neoplasms of histiocytic differentiation. Our aim was to test the ability of CD163 to separate cutaneous histiocytomas from their morphologic mimics. We tested the expression of CD163 in 78 cases, including 19 xanthogranulomas, 16 atypical fibroxanthomas, 6 reticulohistiocytomas, 8 epithelioid cell histiocytomas, 9 cases of Langerhans cell histiocytosis, 10 xanthomas, and 10 intradermal Spitz nevi. CD163 expression was seen in all xanthogranulomas and reticulohistiocytomas, 4 epithelioid cell histiocytomas, 2 cases of Langerhans cell histiocytosis, and 8 xanthomas but was absent in atypical fibroxanthomas and Spitz nevi. CD163 is an excellent marker for confirming histiocytic differentiation and is useful in eliminating morphologic mimics such as Spitz nevi from the differential diagnosis. The lack of CD163 in atypical fibroxanthomas argues against a histiocytic origin for this tumor.

Juvenile xanthogranuloma masquerading as melanoma

Juvenile xanthogranuloma (JXG) of the uvea is a rare disease that usually responds to systemic steroids or low-dose radiotherapy. We present an atypical case of bilateral JXG involving the entire uveal tract that presented with an aggressive phenotype. The patient was unresponsive to topical and systemic corticosteroids, cyclosporine, and maximal doses of radiation therapy. The disease was ultimately controlled with the alkylating agent chlorambucil.

Renal cell carcinoma marker (RCC-Ma) is specific for cutaneous metastasis of renal cell carcinoma

BACKGROUND

Renal cell carcinoma marker (RCC-Ma) is a monoclonal antibody against a normal renal proximal tubule antigen. RCC-Ma expression is relatively specific for primary clear cell renal cell carcinoma. Its expression in cutaneous metastasis of renal cell carcinoma (MRCC) and other cutaneous clear cell lesions has not been studied.

METHODS

One hundred and thirty-seven cutaneous clear cell lesions including eight xanthomas, 32 xanthelasmas, 25 xanthogranulomas, seven balloon cell nevi, six clear cell hidradenomas, 29 sebaceous adenomas, six sebaceous epitheliomas, eight sebaceous carcinomas, and 16 MRCC were examined using immunohistochemistry for the expression of RCC-Ma.

RESULTS

RCC-Ma was expressed in 10 of 16 (62.5%) MRCC, all with greater than 20% of cell labeling. Of these, 4 of 10 (40%) labeled with a membranous pattern and 6 of 10 (60%) labeled with both a membranous and a cytoplasmic pattern. RCC expression was not seen in any of the other clear cell lesions (p < 0.001). Furthermore, lack of expression in each of the other diagnostic groups was significant when each group was compared with the MRCCs (p < 0.01 at least for each group).

CONCLUSIONS

Our study demonstrates that RCC may be a valuable component of a panel of immunohistochemical markers when evaluating cutaneous clear cell lesions.

Reticulohistiocytoma (Solitary Epithelioid Histiocytoma)

Reticulohistiocytoma and multicentric reticulohistiocytosis are designations for uncommon, incompletely characterized histiocytic proliferations of the skin or soft tissues. In this study, we analyzed a uniform group of 44 lesions composed of epithelioid histiocytes, comprising a subset of lesions originally designated as reticulohistiocytoma, and propose designating them as "solitary epithelioid histiocytoma" (SEH), in line with the recently published classification proposal for histiocytic disorders. There were 26 males and 18 females with a median age of 35 years (range, 2.5-74 years). All patients had a superficial, circumscribed, mildly elevated, solitary lesion (size range, 1.5-11 mm; median, 4 mm), located in the trunk wall (n = 16), lower extremity (n = 12), head and neck (n = 8, including 2 in the oral cavity), upper extremity (n = 6), penis (n = 1), and an unspecified site (n = 1). Histologically, the lesions typically involved upper and mid-dermis and were not ulcerated. They were composed of large epithelioid histiocytes with a varying number of lymphocytes and neutrophils. The histiocytes had abundant, typically densely eosinophilic, cytoplasm and mostly mild, if any, nuclear atypia. Multinucleated forms with randomly oriented nuclei were also present. The histiocytes had low mitotic activity (range, 0-4 mitoses per 10 wide HPFs; median, 1 mitosis per 10 HPFs). The lesions contained varying numbers of CD3-positive T cells, whereas B lymphocytes, plasma cells, eosinophils, and mast cells were scant, if present at all. Immunohistochemically, the epithelioid histiocytes were positive for CD163, CD68, lysozyme (variably), and vimentin. They often had focal nuclear immunoreactivity for microphthalmia transcription factor, and they sometimes had focal reactivity for Factor XIIIa and S-100 protein. Membrane positivity for CD31, CD43, and CD45 was variable. The epithelioid histiocytes were consistently negative for CD3, CD20, CD30, HMB45, and keratins. All 12 patients with follow-up information had an uneventful clinical course with no recurrences (median, 13 years). SEH is a benign, probably reactive, histiocytic proliferation of unknown etiology. It needs to be distinguished from Rosai-Dorfman disease, juvenile xanthogranuloma, a variety of granulomatous conditions, and some malignant neoplasms, including histiocytic sarcoma, melanoma, and epithelioid sarcoma.

CD10 is expressed in cutaneous clear cell lesions of different histogenesis

BACKGROUND

CD10, the Common Acute Lymphoblastic Leukemia Antigen, is a neutral endopeptidase commonly used as a marker of early B-cell differentiation in the classification of lymphomas. Neoplasms of other histogenesis may express CD10, including renal cell carcinoma. Renal cell carcinoma metastatic to the skin (MRCC) can simulate other more common clear cell lesions in which expression of CD10 has not been described.

METHODS

Fifty-two cutaneous clear cell lesions including xanthomas (CX), xanthelasmas (XA), xanthogranulomas (XG), balloon cell nevi (BCN), nodular/clear cell hidradenomas (CCH), and MRCC were examined by immunohistochemistry for the expression of CD10, noting frequency and pattern of labeling.

RESULTS

CD10 was expressed in 32/35 of the xanthomatous lesions (CX, XA, and XG), 3/3 MRCC, but only 2/8 BCN and 2/6 CCH. BCN and CCH expressed CD10 in fewer than 10% of the clear cells, whereas all MRCC and most xanthomatous lesions had labeling in greater than 10% (p < 0.001). Xanthomatous lesions exhibited a predominantly membranous pattern of labeling compared to the cytoplasmic pattern of MRCC (p < 0.025).

CONCLUSIONS

Cutaneous clear cell lesions of different histogenesis express CD10, limiting its use as a specific diagnostic marker for MRCC. Among other clear cell lesions, however, BCN and CCH have a lower frequency of labeling than does MRCC, and xanthomatous lesions show a membranous pattern compared to the cytoplasmic pattern of MRCC, BCN, and CCH. This latter observation may be indicative of altered protein function or trafficking.

Intramuscular Juvenile Xanthogranuloma in an Adult

Juvenile xanthogranuloma (JXG) is a self-limited cutaneous lesion that most often occurs in infancy. Approximately 10% to 30% of JXGs occur in adult patients, where most cases present as cutaneous papulonodular lesions, with only rare cases involving extracutaneous sites. Intramuscular JXG is extremely rare and has received little attention. On review of the literature, all of the 6 previously reported intramuscular JXGs were noted in the pediatric population. The authors hereby describe a case of adult intramuscular JXG that occurred in a woman who initially had a dermal JXG in the nasal skin at the age of 48 years and then developed a slow-growing painless intramuscular JXG in the right forearm 4 years later. Both the dermal and intramuscular lesions revealed similar histologic features and consisted of diffuse infiltrates of histiocytes with eosinophilic and foamy cytoplasm, lymphocytes, eosinophils, and Touton giant cells in varying proportions. However, central fibrosis and a focal storiform arrangement of spindled fibroblast-like cells in the intramuscular lesion resulted in a histologic pattern reminiscent of a fibrous histiocytoma. Immunohistochemically, the intramuscular JXG was positive for CD68, factor XIIIa, CD31, and vimentin. This case underscores the fact that intramuscular JXG can also involve adult patients and its morphologic variation is more likely to be time dependent rather than site specific or age related.

Non-melanocytic lesions mimicking melanocytic lesions

Distinction between benign and malignant melanocytic lesions commonly represents a big challenge for the pathologist. Equally difficult is separating tumours with melanocytic lineage from those displaying other lines of differentiation. This is because benign and malignant melanocytic lesions are able to display a wide range of histological appearances that frequently closely mimic reactive and neoplastic lesions (benign and malignant). This applies to processes with almost any line of differentiation. Difficulties in differential diagnosis are mainly found in melanocytic lesions restricted to the dermis or those in which the junctional component is minimal. Although purely junctional melanocytic lesions less commonly pose a problem in differential diagnosis, they may be very problematic, especially in small biopsies. Immunohistochemistry is usually a very important aid in the differential diagnosis of mimics of melanocytic lesions but pitfalls often occur. This is particularly true when small samples are analysed and when close clinicopathological correlation is lacking. This review discusses the histological differential diagnosis of mimics of melanocytic lesions. These mimics are separated into those primarily presenting in the epidermis and those presenting in the dermis.

The histiocytic marker PG-M1 is helpful in differentiating histiocytes and histiocytic tumors from melanomas

Previous studies have shown that immunohistochemical stains for histiocytes are immunoreactive for melanomas. Accordingly, their value in differentiating histiocytes and histiocytic lesions from melanomas was questioned. PG-M1, the most specific histiocytic marker, was not evaluated in these studies. Our aims were to assess the reactivity of PG-M1 with a series of primary cutaneous and metastatic melanomas and to establish the potential usefulness of this antibody in the differentiation between histiocytes and histiocytic tumors and melanomas. PG-M1 staining was performed in 50 primary cutaneous and metastatic melanomas. For comparison, additional sections were stained with KP-1 and lysozyme (commonly used as histiocytic markers) and with S-100 and HMB-45 (commonly used as melanoma markers). The intensity (1+, 2+) and extent (1+ to 4+) were recorded semiquantitatively. PG-M1 stained weakly (1+) and focally (2+) only four cases of melanoma (8%). In contrast, histiocytes were strongly reactive for PG-M1 in all cases, being readily differentiated from melanoma cells including the positive cases. KP-1 stained melanoma cells in 44 cases (88%), lysozyme in 11 cases (22%), S-100 in 50 cases (100%), and HMB-45 in 48 cases (96%). No changes were found after restaining of selected KP-1 and lysozyme positive melanomas using an endogenous avidin/biotin blocking kit. PG-M1 is helpful in discriminating histiocytes and histiocytic lesions from melanoma cells. We recommend its inclusion in any antibody panel put together to distinguish between them.

Expression of melanocytic differentiation markers in malignant melanomas of the oral and sinonasal mucosa

Malignant melanomas of the oral and sinonasal mucosa are rare tumors. Amelanotic variants can, on occasion, be difficult to recognize by routine light microscopy. Immunohistochemical studies may be needed for a final diagnosis. A number of new monoclonal antibodies to melanocytic differentiation antigens have been studied recently on primary cutaneous and metastatic melanoma. However, little is known about these antibodies for the diagnosis of mucosal melanomas. In this study the authors analyzed 79 oral and sinonasal mucosal melanomas of 65 patients. A total of 35 tumors originated from the oral mucosa (21 primary tumors, eight local recurrences, and six metastases) and 44 melanomas were from the sinonasal tract (27 primary tumors, nine local recurrences, and eight metastases). Immunohistochemical studies were performed on paraffin-embedded tissues, using the following antibodies: anti-S-100 protein, T311 (anti-tyrosinase), A103 (anti-Mart-1/Melan-A), D5 (antimicrophthalmia-associated transcription factor), and HMB-45 (anti-gp100). Of 35 oral mucosal tumors, 34 (97%) were positive with anti-S-100 protein, 33 (94%) with T311, 30 (85%) with A103, 26 (74%) with D5, and 25 (71%) with HMB-45. All five desmoplastic melanomas of the oral mucosa were positive for S-100 protein, four for tyrosinase, and one each for HMB-45 and A103. No desmoplastic melanoma was positive with D5. All 44 sinonasal melanomas were positive for tyrosinase and Mart-1/Melan-A (100%). Forty-three (98%) were positive with HMB-45, 42 (95%) with anti-S-100 protein, and 40 (91%) with D5. These results reveal that T311 is the most sensitive marker for sinonasal melanomas and closely approaches the sensitivity of anti-S-100 protein for oral mucosal melanomas. For desmoplastic mucosal tumors, anti-S-100 protein remains the most sensitive marker.

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

Microphthalmia transcription factor (Mitf) is a nuclear protein involved in the development of melanocytes and the regulation of melanin synthesis. Recent studies have suggested that Mitf may be a more sensitive and specific melanocyte marker than S-100 protein and gp100. However, there is insufficient knowledge on the specificity of Mitf, and a systematic examination of its use for the recognition of desmoplastic melanoma has not yet been performed. In this study, we compared the expression of Mitf with S-100 protein, gp100, and tyrosinase in 20 desmoplastic melanomas by using the antibodies D5 (anti-Mitf), anti-S100P, HMB-45 (anti-gp100), and T311 (anti-tyrosinase). All 20 melanomas were positive for S-100 protein, 7 were positive for Mitf, 6 for gp100, and 11 for tyrosinase. To examine the specificity of Mitf, a panel of normal tissue and 386 samples of miscellaneous tumors, including dermal and subcutaneous spindle cell lesions relevant for the differential diagnosis of desmoplastic melanoma, were examined by immunohistochemistry. Furthermore, normal tissue samples were tested for Mitf mRNA by reverse transcriptase polymerase chain reaction (rt-PCR). Immunoreactivity for Mitf was seen not only in melanocytes of normal skin, but also in macrophages, lymphocytes, fibroblasts, Schwann cells, and smooth muscle cells at various sites, and tumors derived thereof. Our results indicate that the antibody D5 lacks sufficient sensitivity and specificity for widespread diagnostic use. Especially in re-excisions, when immunohistochemistry is often needed to distinguish an inflamed scar tissue from tumor, the presence of immunopositive inflammatory cells and fibroblasts limits the diagnostic use of D5.

Microphthalmia transcription factor in the immunohistochemical diagnosis of metastatic melanoma: comparison with four other melanoma markers

The diagnosis of metastatic malignant melanoma (MMM) may be difficult in surgical pathology, often complicated by the unpredictable spread of this tumor and its great variability on histologic evaluation. Traditionally used immunohistochemical markers on melanomas are insufficient because of either a relative lack of specificity (S100 protein) or variably reported sensitivity (HMB45). Information about some newer markers, such as tyrosinase (TYR) and Melan A, is more limited. Recently, based on the study of a small number of tumors, it was suggested that microphthalmia transcription factor (MITF) is 100% sensitive in the identification of metastatic melanoma. In the current study, we compared the diagnostic usefulness of MITF with that of four other markers in 266 cases of conventional metastatic melanomas from different sites, 33 cases of desmoplastic melanomas, and 1 case of melanoma with rhabdoid features. The specificity of MITF was evaluated by using a representative sample of control tumors. Microphthalmia transcription factor with nuclear positivity was seen in 235 of 266 cases of conventional MMM (88%), usually in more than 30% of tumor cells. However, some melanomas had only foci of MITF- and TYR-positive cells, whereas the majority of cells were generally S100 protein-positive. Only 1 of 30 desmoplastic melanomas (3%) had MITF-positive cells, representing epithelioid foci resembling conventional melanoma. Two cases had TYR in a similar pattern; all were HMB45-negative. One metastatic melanoma with rhabdoid features was negative for MITF and other markers except the S100 protein. Half of the S100 protein negative conventional melanomas (6 of 12) were MITF-positive, whereas 4 of 20 (20%) TYR-negative tumors had reactivity for MITF. The percentages of positive cases of MMM (10% or more tumor cells positive) diagnosed with the four other markers in descending order were 90% (S100 protein and TYR), 78% (melan-A), and 66% (HMB45). Microphthalmia transcription factor appeared to be specific, because significant reactivity was not found in 112 carcinomas, 20 lymphomas, 20 angiosarcomas, 20 fibrous histiocytomas, and 20 malignant peripheral nerve sheath tumors. However, positive nuclei were found focally among reactive histiocytes, especially in osteoclasts, epithelioid histiocytes, and sporadic other histiocytes. Microphthalmia transcription factor may be a valuable addition to the marker panel used in diagnosing melanoma, in combination with S100, TYR, and the other markers, but it is not present in cases of desmoplastic melanomas.