Amelanotic Melanoma Research Articles

Amelanotic Melanoma-Biochemical and Molecular Induction Pathways.

Amelanotic melanoma (AM) is a subtype of hypomelanotic or completely amelanotic melanoma. AM is a rare subtype of melanoma that exhibits a higher recurrence rate and aggressiveness as well as worse surveillance than typical melanoma. AM shows a dysregulation of melanin production, cell cycle control, and apoptosis pathways. Knowing these pathways has an application in medicine due to targeted therapies based on the inhibiting elements of the abovementioned pathways. Therefore, we summarized and discussed AM biochemical and molecular induction pathways and personalized medicine approaches, clinical management, and future directions due to the fact that AM is relatively rare. AM is commonly misdiagnosed. Hence, the role of biomarkers is becoming significant. Nonetheless, there is a shortage of biomarkers specific to AM. BRAF, NRAS, and c-KIT genes are the main targets of therapy. However, the role of BRAF and KIT in AM varied among studies. BRAF inhibitors combined with MAK inhibitors demonstrate better results. Immune checkpoint inhibitors targeting CTLA-4 combined with a programmed death receptor 1 (PD-1) show better outcomes than separately. Fecal microbiota transplantation may overcome resistance to immune checkpoint therapy of AM. Immune-modulatory vaccines against indoleamine 2,3-dioxygenase (IDO) and PD ligand (PD-L1) combined with nivolumab may be efficient in melanoma treatment.

The Role of Digital Dermoscopy and Follow-Up in the Detection of Amelanotic/Hypomelanotic Melanoma in a Group of High-Risk Patients-Is It Useful?

The prognosis, outcome, and overall survival of melanoma patients improve with early diagnosis which has been facilitated in the past few decades with the introduction of dermoscopy. Further advancements in dermoscopic research, coupled with skilled, educated dermatologists in dermoscopy, have contributed to timely diagnoses. However, detecting amelanotic and hypomelanotic melanoma remains a challenge even to the most skilled experts because these melanomas can mimic inflammatory diseases, numerous benign lesions, and non-melanoma skin cancers. The list of the possible differential diagnoses can be long. Melanoma prediction without the pigment relies only on vascular criteria, and all classic dermoscopic algorithms have failed to fulfill our expectations. In fact, the diagnosis of amelanotic and hypomelanotic melanomas is very challenging, which is why every tool in detecting these lesions is of significance. This review aims to explore the current knowledge and the literature on the possibility of detecting amelanotic/hypomelanotic melanomas using sequential monitoring with digital dermoscopy and total body skin photography.

Role of albinism and pigment-related genes in amelanotic melanoma formation.

Role of albinism and pigment-related genes in amelanotic melanoma formation.

Unilateral amelanotic conjunctival malignant melanoma: a case report

IntroductionCutaneous malignant melanomas rarely occur in the eye, usually in the eyelids or the conjunctiva. Conjunctival malignant melanomas are even rarer. Most melanomas are dark in color as they are pigmented. However, amelanotic conjunctival malignant melanomas, a scarce variant of the cancer, can be challenging to diagnose accurately.Case presentationWe present two cases of white Caucasian Swedish-born women who were diagnosed with unilateral amelanotic malignant melanoma in the conjunctiva of the eye. In the first case, the patient was an 81-year-old woman who was suffering from redness and foreign body sensation in the left eye. The initial diagnosis was blepharitis. Three biopsies were taken, which showed malignant melanoma in the eyelid and the conjunctiva. Unfortunately, the eye and the rest of the orbit could not be saved, and the patient had to undergo an orbital exenteration. In the second case, the patient was a 50-year-old woman, and the tumor was localized in the temporal conjunctiva of the left eye. The initial diagnosis was pinguecula, but at the time of surgery, the physician suspected conjunctival intraepithelial neoplasia. The tumor was not completely removed, so adjuvant brachytherapy and local chemotherapy were used. The eye was preserved. No neck and/or lung metastasis was detected in either case at the time of diagnosis.ConclusionsConjunctival amelanotic malignant melanomas should be suspected when tumors are present in the eye and/or the eyelids. By suspecting amelanotic malignant melanoma, the delay in treatment can be shortened. Treating them as soon as possible is essential to minimize the risk of metastasis.

Impact of Demographics on Early-Stage vs. Stage IV Diagnosis in Amelanotic Melanoma: An Analysis of the National Cancer Database.

Introduction Amelanotic melanoma (AM) is a rare form of melanoma that lacks pigment. Although curable when diagnosed early, it is often missed or mistaken for other benign conditions. There has not been a study investigating the impact of demographic features on the diagnosis of stage 0-I (early-stage) versus stage IV AM. Objective This study addresses a gap in knowledge regarding demographic factors that influence the odds of early-stage vs. stage IV diagnosis of AM. Methods This study identified 684 patients from the National Cancer Database who were diagnosed with early-stage AM or stage IV AM from 2004 to 2020 and compared them based on age, sex, race, insurance, income, education, insurance status, rurality, facility type, geographic region, and Charleson-Deyo score. Socioeconomic and demographic features of patients with early-stage and stage IV were compared using the chi-squared test, the independent t-test, and multivariate logistic regression. Statistical significance was set at α = 0.05. Results Most cases analyzed were White (98.5%), male (57.7%), and lived in a metropolitan setting (86.7%). Males made up most of the early-stage and stage IV groups (55.0% vs. 45% and 66.5% vs. 33.5%, respectively, p < 0.05). Younger age is associated with decreased odds of stage IV disease (OR = 0.973, 95% CI = 0.952-0.993, p < 0.05). In addition, the female sex is associated with decreased odds of stage IV disease (OR = 0.584, 95% CI = 0.381-0.897, p < 0.05). Conclusions Age and sex are two variables that influence the odds of stage IV diagnosis in patients with AM, which is strongly associated with worse survival outcomes.

54167 The Effects of an Educational Video on Patient Understanding of Amelanotic Melanoma

54167 The Effects of an Educational Video on Patient Understanding of Amelanotic Melanoma

Reflectance Confocal Microscopy and Dermoscopy for the Diagnosis of Solitary Hypopigmented Pink Lesions: A Narrative Review.

Diagnosing solitary pink skin lesions poses a significant challenge due to the scarcity of specific clinical and dermoscopic criteria. Several benign lesions, such as cherry angioma, clear cell acanthoma, dermal nevus, keloid, hypertrophic scar, and Spitz nevus, often exhibit similar clinical and dermoscopic features. This similarity extends to some malignant lesions, including basal cell carcinoma, actinic keratosis, and amelanotic melanoma, making differentiation difficult. Recent studies highlight the enhanced diagnostic accuracy of reflectance confocal microscopy (RCM), which offers increased sensitivity and specificity compared to dermoscopy alone for diagnosing skin cancer. This study aims to summarize the application of dermoscopy and RCM in distinguishing between benign and malignant pinkish-reddish skin lesions. The integration of RCM with traditional dermoscopic techniques improves the ability to accurately identify and differentiate these lesions. However, it is crucial to note that for any suspicious lesions, a final diagnosis must be confirmed through surgical excision and histopathological evaluation. This comprehensive approach ensures accurate diagnosis and appropriate treatment, highlighting the importance of combining advanced imaging techniques in clinical practice.

Design, Synthesis, and Anticancer and Antibacterial Activities of Quinoline-5-Sulfonamides.

A series of new unique acetylene derivatives of 8-hydroxy- and 8-methoxyquinoline- 5-sulfonamide 3a-f and 6a-f were prepared by reactions of 8-hydroxy- and 8-methoxyquinoline- 5-sulfonyl chlorides with acetylene derivatives of amine. A series of new hybrid systems containing quinoline and 1,2,3-triazole systems 7a-h were obtained by reactions of acetylene derivatives of quinoline-5-sulfonamide 6a-d with organic azides. The structures of the obtained compounds were confirmed by 1H and 13C NMR spectroscopy and HR-MS spectrometry. The obtained quinoline derivatives 3a-f and 6a-f and 1,2,3-triazole derivatives 7a-h were tested for their anticancer and antimicrobial activity. Human amelanotic melanoma cells (C-32), human breast adenocarcinoma cells (MDA-MB-231), and human lung adenocarcinoma cells (A549) were selected as tested cancer lines, while cytotoxicity was investigated on normal human dermal fibroblasts (HFF-1). All the compounds were also tested against reference strains Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212 and representatives of multidrug-resistant clinical isolates of methicillin-resistant S. aureus (MRSA) and vancomycin-resistant E. faecalis. Only the acetylene derivatives of 8-hydroxyquinoline-5-sulfonamide 3a-f were shown to be biologically active, and 8-hydroxy-N-methyl-N-(prop-2-yn-1-yl)quinoline-5-sulfonamide (3c) showed the highest activity against all three cancer lines and MRSA isolates. Its efficacies were comparable to those of cisplatin/doxorubicin and oxacillin/ciprofloxacin. In the non-cancer HFF-1 line, the compound showed no toxicity up to an IC50 of 100 µM. In additional tests, compound 3c decreased the expression of H3, increased the transcriptional activity of cell cycle regulators (P53 and P21 proteins), and altered the expression of BCL-2 and BAX genes in all cancer lines. The unsubstituted phenolic group at position 8 of the quinoline is the key structural fragment necessary for biological activity.

Dermal melanoma with plasmacytoid differentiation in a dog.

A 10-y-old spayed female Staffordshire Terrier dog was evaluated because of a cutaneous left ear base mass. Cytology revealed sheets of cells with anisocytosis and anisokaryosis, round-to-oval or plasmacytoid cytoplasm, and round, central, or eccentric nuclei; binucleate cells were present. Cytologic findings were consistent with a round cell tumor (plasmacytoma or agranular mast cell tumor), amelanotic melanoma, or anaplastic carcinoma. Histologically, neoplastic cells were polygonal to elongate, with round-to-oval nuclei and prominent nucleoli and arranged in sheets and nests on a fibrovascular stroma. Neoplastic cells with plasmacytoid morphology (round, glassy, eosinophilic cytoplasm with eccentric nuclei) were present in ~30% of the neoplasm. There were 18 mitoses in 2.37 mm2 (10 FN22/40× fields). Neoplastic cells had cytoplasmic immunolabeling for melan A and PNL2 and no immunolabeling for AE3/1 and MUM1, consistent with a dermal melanoma with plasmacytoid differentiation. The patient was re-evaluated ~1 mo after the first biopsy because of local recurrence of the original mass and new masses on the interscapular area and right elbow; these neoplasms were histologically identical to the original submission, plus scattered neoplastic cells in the new masses contained brown cytoplasmic pigment. The dog was euthanized because of swelling and hemorrhage of the tumors and right pelvic limb lameness. Our findings were consistent with a dermal melanoma with plasmacytoid features that were similar to human plasmacytoid melanoma, a rare variant of human melanoma that is diagnostically challenging as it may mimic a plasmacytoma.

Clinical and Multimodal Imaging Study to Differentiate Amelanotic Choroidal Lesions

Introduction: The aim of this study was to differentiate amelanotic choroidal lesions – amelanotic choroidal melanoma, choroidal metastasis, and choroidal granuloma using multimodal imaging. Methods: Retrospective comparative chart review was done. Patients diagnosed with the abovementioned choroidal lesions from 2015 to 2022 were included. Baseline lesion morphology and retinal layer changes on optical coherence tomography (OCT), lesion echogenicity and dimensions on ocular ultrasonography (USG), fundus autofluorescence (FAF), fundus fluorescein angiography (FFA), and indocyanine green angiography (ICG-A) patterns and findings were assessed. Results: Twelve eyes with melanoma, 22 eyes with metastasis, and 9 eyes with granuloma were included. On OCT, 83% of melanomas and 67% of granulomas, and 68% of metastasis had dome-shaped choroidal lesions. Presence of intraretinal fluid (IRF) and shaggy photoreceptors was 94% (95% CI: 79–99%) and 90% (95% CI: 74–98%) specific to differentiate melanomas from other choroidal lesions (AUC >0.75, p < 0.05). Similarly, presence of incomplete retinal pigment epithelium (RPE) and outer retinal atrophy (iRORA) was 77% (95% CI: 55–92%) sensitive and 77% (95% CI: 53–92%) specific (AUC = 0.8, p+ 0.03) and presence of lumpy-bumpy choroid was 55% (95% CI: 32–76%) sensitive and 95% (95% CI: 76–99%) specific (AUC = 0.75, p = 0.04) to distinguish metastasis from other choroidal lesions. Mean height: base ratio was more in melanoma compared to metastasis (0.54 ± 0.22 vs. 0.43 ± 0.12, p = 0.17) and both were hyperechoic on USG. On FAF, 100% metastasis and 60% granulomas were hypoAF, whereas 100% melanomas were hypoAF. Majority choroidal lesions were hyperfluorescent on FFA. Double vascular circulation was observed in melanomas (50%). On ICG-A, all choroidal lesions were hypofluorescent. Conclusion: Clinical and multimodal imaging features such as the presence of IRF, shaggy photoreceptors, iRORA, and lumpy-bumpy choroid can help diagnose and differentiate amelanotic choroidal lesions, thereby avoiding the need for choroidal biopsy. Further larger studies are needed to devise a standard imaging protocol to validate our findings.

Thin Amelanotic and Hypomelanotic Melanoma: Clinicopathological and Dermoscopic Features.

Background and Objectives: Amelanotic/hypomelanotic melanomas (AHMs) account for 2-8% of all cutaneous melanomas. Due to their clinical appearance and the lack of specific dermoscopic indicators, AHMs are challenging to diagnose, particularly in thinner cutaneous lesions. The aim of our study was to evaluate the clinicopathological and dermoscopic features of thin AHMs. Identifying the baseline clinical-pathological features and dermoscopic aspects of thin AHMs is crucial to better understand this entity. Materials and Methods: We divided the AHM cohort into two groups based on Breslow thickness: thin (≤1.00 mm) and thick (>1.00 mm). This stratification helped identify any significant clinicopathological differences between the groups. For dermoscopic analysis, we employed the "pattern analysis" approach, which involves a simultaneous and subjective assessment of different criteria. Results: Out of the 2.800 melanomas analyzed for Breslow thickness, 153 were identified as AHMs. Among these, 65 patients presented with thin AHMs and 88 with thick AHMs. Red hair color and phototype II were more prevalent in patients with thin AHMs. The trunk was the most common anatomic site for thin AHMs. Patients with thin AHMs showed a higher number of multiple melanomas. Dermoscopic analysis revealed no significant difference between thin AHMs and thick AHMs, except for a more frequent occurrence of residual reticulum in thin AHMs. Conclusions: Thin AHMs typically affect individuals with lower phototypes and red hair color. These aspects can be related to the higher presence of pheomelanin, which provides limited protection against sun damage. This also correlates with the fact that the trunk, a site commonly exposed to intermittent sun exposure, is the primary anatomical location for thin AHMs. Multiple primary melanomas are more common in patients with thin AHMs, likely due to an intrinsic predisposition as well as greater periodic dermatologic follow-ups in this class of patients. Apart from the presence of residual reticulum, no other significant dermoscopic differences were observed, complicating the differential diagnosis between thin and thick AHMs based on dermoscopy alone.

Amelanotic Melanoma: A Rare Sinonasal Malignancy.

Mucosal melanomas account for less than 1% of all sinonasal malignancies and are aggressive tumours originating from melanocytes in various mucosal epithelia. Diagnosis is often delayed due to nonspecific symptoms, contributing to challenges in treatment and management. We present a case of a 75-year-old female with epistaxis and nasal blockage, ultimately diagnosed with amelanotic sinonasal melanoma. Despite diagnostic difficulties exacerbated by profuse bleeding during biopsy attempts, a comprehensive approach involving clinical evaluation, imaging, and histopathology led to a definitive diagnosis. Immunohistochemistry played a crucial role in confirming the diagnosis, ruling out differential diagnoses such as olfactory neuroblastoma and lymphoma. Surgical excision, despite intraoperative bleeding, was successful, followed by adjuvant chemotherapy and radiotherapy due to the tumor's advanced stage. The case underscores the importance of a multidisciplinary approach and personalized treatment strategies, considering the tumor's molecular characteristics for improved outcomes in managing this rare malignancy.

DP20 A case series identifying the clinical and histopathological characteristics of amelanotic melanoma

DP20 A case series identifying the clinical and histopathological characteristics of amelanotic melanoma

Spatial transcriptomic analysis of amelanotic acral melanoma versus pigmented acral melanoma reveals distinct molecular determinants.

Amelanotic acral melanoma (AAM) is a rare type of acral melanoma that has a poor prognosis. To investigate the transcriptomic differences between AAM and pigmented acral melanoma (PAM). Differences in the spatially resolved transcriptomic profiles of 9 patients with AAM with 29 regions of interest (ROIs) and 11 patients with PAM with 46 ROIs were investigated using S100b and CD3 morphology markers. In S100b+ tumour cell areas, we detected 11 upregulated differentially expressed genes (DEGs; including chaperone/ubiquitin--associated DEGs) and 82 downregulated DEGs (including human leucocyte antigen) in AAMs vs. PAMs. Protein-protein interaction network and pathway analyses revealed significant enrichment of dysregulated translational and nonsense-mediated decay pathways but significant decreases in antigen processing and presentation, interferon signalling and melanin biosynthesis pathways in S100b+ ROIs of AAMs compared with PAMs. In tumour-associated immune cell areas, the numbers of CD8 T cells (P = 0.04) and M1 macrophages (P = 0.01) were significantly decreased, whereas those of monocytes (P = 0.04) and endothelial cells (P = 0.04) were increased in AAMs compared with PAMs. These findings could widen our understanding of the biological differences between AAMs and PAMs, which might result in a different clinical course.

Hyaluronic Acid/Ellagic Acid as Materials for Potential Medical Application.

The aim of this work was to develop and characterize a thin films composed of hyaluronic acid/ellagic acid for potential medical application. Its principal novelty, distinct from the prior literature in terms of hyaluronic acid films supplemented with phenolic acids, resides in the predominant incorporation of ellagic acid-a distinguished compound-as the primary constituent of the films. Herein, ellagic acid was dissolved in two different solvents, i.e., acetic acid (AcOH) or sodium hydroxide (NaOH), and the surface properties of the resultant films were assessed using atomic force microscopy and contact angle measurements. Additionally, various physicochemical parameters were evaluated including moisture content, antioxidant activity, and release of ellagic acid in phosphate buffered saline. Furthermore, the evaluation of films' biocompatibility was conducted using human epidermal keratinocytes, dermal fibroblasts, and human amelanotic melanoma cells (A375 and G361), and the antimicrobial activity was elucidated accordingly against Staphylococcus aureus ATCC 6538 and Pseudomonas aeruginosa ATCC 15442. Our results showed that the films exhibited prominent antibacterial properties particularly against Staphylococcus aureus, with the 80HA/20EA/AcOH film indicating the strong biocidal activity against this strain leading to a significant reduction in viable cells. Comparatively, the 50HA/50EA/AcOH film also displayed biocidal activity against Staphylococcus aureus. This experimental approach could be a promising technique for future applications in regenerative dermatology or novel strategies in terms of bioengineering.

Canine Oral Melanoma: Questioning the Existing Information through a Series of Clinical Cases.

Twelve dogs with oral malignant melanomas (MM) were evaluated in this study, with demographic details indicating a balanced distribution of gender, age, and weight among various breeds. Tumor locations varied, with diverse surgical procedures being performed, including mandibulectomies and maxillectomies. Lymphadenectomies were conducted, revealing a 16.66% metastatic rate in regional lymph nodes. At the time of surgery, clinical staging identified stages I, II, and III, with most cases having non-infiltrated margins and a high mitotic index. Follow-up revealed local recurrences and metastases, prompting additional surgeries and affecting survival rates. This study reports varying outcomes, with some dogs completing one year without recurrence, while others experienced progressive disease, leading to six oral melanoma-related deaths. The characteristics of melanotic melanoma and amelanotic melanoma are observed in order to study differences between them, the degree of aggressiveness, the mortality rate and the possibility of future therapeutic targets. Although high pigmentation has been correlated with a better outcome, we could not find any significant correlation between survival and achromia. Oral benign melanomas might exist, and this could justify variabilities between stage and survival; however, carefulness is required due to their unpredictable behavior. The findings underscore the complexity of oral melanoma cases and highlight the need for further research on effective management strategies.

Misdiagnosis and Clinical Insights into Acral Amelanotic Melanoma-A Systematic Review.

Acral amelanotic melanomas (AAMs), a rare subset of melanomas located on acral sites such as the palms, soles, and subungual areas, are diagnostically challenging due to their lack of typical pigmentation and often benign clinical appearance. Misdiagnosis is common, leading to delays in treatment and potentially worse outcomes. This systematic review aims to synthesise evidence on cases of AAM initially misdiagnosed as other conditions, to better understand their clinical and epidemiological characteristics, diagnostic pitfalls, and management strategies. A comprehensive search of the MEDLINE/PubMed, EMBASE, and SCOPUS databases was conducted up to March 2024. Case reports and small case series of AAMs initially misdiagnosed as other conditions were included. Data on patient demographics, clinical presentation, and diagnostic methods were collected and analyzed. Of the 152 records identified, 26 cases from 23 articles met the inclusion criteria. A demographic analysis revealed that the gender distribution appears to be perfectly balanced, with an age range of 38 to 91 years. Misdiagnoses included non-healing ulcers or traumatic lesions (37.5%), benign proliferative lesions (29.2%) and infectious lesions (20.8%). The foot was the most affected site (53.8%). Notably, a histological evaluation was performed in 50% of cases involving the upper extremities, in contrast to only 7.1% of cases involving the foot and 0% of cases of the heel. This discrepancy suggests a reluctance to perform biopsies in the lower extremities, which may contribute to a higher misdiagnosis rate in these areas. The underutilization of biopsy in the diagnosis of lower extremity lesions contributes significantly to the misdiagnosis and delay in treatment of AAMs. Especially when the clinical assessment and dermoscopy are inconclusive, biopsies of suspicious lesions are essential. Immunohistochemistry and markers such as PRAME are critical in differentiating melanoma from other malignancies such as clear cell sarcoma. This review highlights the need for increased vigilance and a proactive diagnostic approach to increase early detection rates and improve prognostic outcomes.

Melanoma amelanótico em cachorro-do-mato (Cerdocyon thous)

The accelerated and disordered division of cells in the body results in neoplastic processes. Melanoma, a malignant neoplasm, is described in domestic dogs, and it has already been reported in wild carnivores. During a routine examination of an adult crab-eating fox (Cerdocyon thous), approximately 14 years old and kept at the Sorocaba Zoo, presented a mass in the perineal region. A surgical procedure was realized to remove the mass, as it presented ulceration. The patient’s recovery was satisfactory and the animal was medically discharged. Cytological, histological and immunohistochemical tests were performed, and the results indicated amelanotic melanoma. This is the first report of amelanotic melanoma in a crab-eating fox kept under human care.

Amelanotic Choroidal Melanoma with Extraocular Extension in a 51 Year-Old Female: A Rare Case

Introduction: Melanoma is a dangerous malignancy primarily involving the choroid, ciliary body, or iris. The most frequent primary intraocular malignant tumor is choroidal melanoma. The tumor most often affects Caucasians of Northern Europe ranging between the ages of 50 and 80. Most choroidal melanomas are pigmented, however, non-pigmented or mixed pigmented and non-pigmented forms can also happen. Compared with other amelanotic choroidal lesions, amelanotic choroidal melanoma showed markedly greater basal diameter, thickness, frequent connection with subretinal fluid, and ultrasonic hollowness. Extrascleral extension is currently detected in 10% to 28% of choroidal melanoma patients, and the mortality rate is much greater than in those without the extension. Case Presentation: We reported a rare case of extraocular extension in a 51-year-old female patient with amelanotic melanoma. The primary complaint was a painful and bleeding mass on her left eye that had developed two months prior to admission. On the conjunctiva of the left eye, there was a solid, palpable mass measuring 4 x 3.5 x 1 cm. It was red, well-defined, and had a hard, solid consistency. It was fixed at the base, had minimal bleeding, and pressed on her eyeball from the inferolateral direction. The cornea appears clear, and there is no light perception in visual acuity. The orbital focus computed tomography scan revealed an Enhancing solid mass containing a fat component. The mass was in the left intraocular, extending from intraconal to extraconal. Conclusions: Amelanotic melanoma with extraocular extension is a rare condition that can be difficult to detect due to its unclear clinical symptoms and wide range of possible causes. Patients and their families must be educated to receive the appropriate first therapy and prevent the illness from worsening. Melanoma management depends on several factors: tumor size, location, related characteristics, opposite eye status, systemic status, and patient preference. Orbital exenteration is one of the management options for choroidal melanoma with significant extraocular extension. By the time ocular treatment begins, the patient's survival may already be predetermined, and this realization could impact how uveal melanoma is treated in the years to come.

Melan-A immunolabeling in canine extramedullary plasmacytomas.

Histologic diagnosis of less well-differentiated cases of canine extramedullary plasmacytomas (CEMPs) may require immunohistochemical confirmation to discriminate these tumors from other round cells tumors including lymphoma, cutaneous histiocytoma, and amelanotic melanomas. CEMPs are characterized by widespread immunoreactivity for multiple myeloma 1 (MUM1) antigen and λ light chains, while the melanocytic marker melan-A has been reported to yield negative results. Here, 33 randomly selected CEMPs, 20 melanocytomas, and 20 malignant melanomas were immunohistochemically tested for MUM1, melan-A, and PNL2. In addition, CEMPs were examined for PAX5, E-cadherin, CD3, CD18, CD20, S100, as well as λ and κ light chain immunoreactivity. All CEMPs were characterized by labeling for MUM1 and λ light chain, as well as variable immunopositivity for the remaining antibodies. Notably, 13 cases of CEMPs (39.4%) exhibited immunolabeling for melan-A. Melanocytic tumors immunolabeled for melan-A (40/40; 100%) and PNL2 (34/40; 85%). An unexpected cytoplasmic immunoreactivity for MUM1 was observed in 2 melanocytic tumors. Summarized, MUM1 or melan-A immunomarkers alone are not sufficient to differentiate between CEMPs and amelanotic melanomas and should be part of a larger immunopanel including λ light chain, CD20, and PNL2.