PRAME expression in 155 cases of metastatic melanoma

Evaluation of PRAME immunohistochemistry in cutaneous vascular neoplasms reveals frequent expression in primary and post-irradiation cutaneous angiosarcomas

BACKGROUND

Preferentially expressed antigen in melanoma (PRAME) has been extensively studied in cutaneous melanocytic tumors and has proven valuable as a diagnostic adjunct in routine dermatopathology practice. However, its expression in cutaneous vascular neoplasms, particularly angiosarcomas (AS), remains largely unexplored.

METHODS

To further explore PRAME expression in cutaneous AS, 18 cases of post-irradiation and 13 cases of primary cutaneous AS were evaluated for PRAME. For comparison, sections from 11 deep soft tissue/visceral AS, 10 Kaposi sarcomas, 8 microvenular hemangiomas, 7 infantile hemangiomas, 8 atypical vascular lesions, 6 epithelioid hemangioendotheliomas, 6 pyogenic granulomas, 6 papillary endothelial hyperplasias, 6 epithelioid hemangiomas, 3 capillovenous malformations, 3 hobnail hemangiomas, 2 spindle cell hemangiomas, 2 pseudomyogenic hemangioendotheliomas, and 2 composite hemangioendotheliomas were also retrieved.

RESULTS

Overall, 22 of 31 (70.9%; 12 post-irradiation and 10 primary) cutaneous AS were positive for PRAME. In contrast, only 1 of 11 (9.1%) deep soft tissue/visceral AS showed diffuse and strong PRAME nuclear staining. All other tumor types were negative for PRAME, except for 5 of 7 (71.4%) infantile hemangiomas, which demonstrated rare (<5%; four cases) and 1+ (5-25%; one case) nuclear staining.

CONCLUSIONS

In this study, we have demonstrated frequent nuclear PRAME expression in cutaneous AS. PRAME immunohistochemistry may serve as a valuable additional marker in selected clinical settings.

Utility of PRAME Immunohistochemistry in the Detection of Subtle Melanoma Microsatellites

ABSTRACT

Microsatellitosis is well established as a prognostic factor in malignant melanoma. Its identification leads to subsequent upstaging with implications for further management. We describe 6 cases in which immunohistochemical staining for PReferentially expressed Antigen in MElanoma facilitated detection of small foci of micrometastasis on scanning magnification, which may be potentially missed in routine sections.

PRAME Expression in Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine tumor of the skin. Risk factors include extensive sun damage, infection with Merkel cell polyomavirus, and an immunocompromised state. PRAME, also known as preferentially expressed antigen in melanoma, is a cancer-testis antigen recently found to be a useful diagnostic tool in the workup of melanocytic neoplasms. However, the expression pattern of PRAME in Merkel cell carcinoma is unknown. In this study, we examine PRAME expression in Merkel cell carcinoma and explore its prognostic implications. The institutional archives at the University of Virginia were used to search for tumors classified as Merkel cell carcinoma from 2004 to 2022. All potential cases were reviewed to confirm the diagnosis, and electronic medical records were searched for clinical and demographic data. Tumors were subsequently immunostained for PRAME and Merkel cell polyomavirus. Cox proportional hazards regression models were used to estimate relative (all-cause) survival of PRAME positivity and MCPyV positivity in our study as well as MCC-specific survival of PRAME positivity. Univariate and multivariable models were created for each outcome related to all-cause survival. A total of 39 cases were included in the study. Twenty-eight percent (11 cases) demonstrated strong PRAME expression, and 27% of cases were positive for Merkel cell polyomavirus. There was no statistically significant correlation between PRAME expression and virus positivity. With respect to PRAME, the adjusted all-cause mortality hazard ratio was 11.4 (95% CI: 1.8, 70.8). The unadjusted MCC-specific hazard ratio was 4.6 (95% CI: 0.8, 27.5). The adjusted hazard ratio pertaining to Merkel cell polyomavirus infection was 0.25 (95% CI: 0.02, 2.96). In this limited cohort, PRAME expression appears to correlate with worse outcomes in Merkel cell carcinoma.

Site-discordant expression of myeloid cell nuclear differentiation antigen in blastic plasmacytoid dendritic cell neoplasm

OBJECTIVES

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare and aggressive hematologic neoplasm that can show clinical, morphologic, and immunophenotypic overlap with acute myeloid leukemia. Myeloid cell nuclear differentiation antigen (MNDA) is a nuclear protein expressed by myelomonocytic cells previously reported to be reliably absent in BPDCN and proposed as a useful adjunct for the distinction of BPDCN and acute myeloid leukemia. We encountered a case of BPDCN that showed strong nuclear expression of MNDA in bone marrow and breast samples and weak to absent expression in skin samples, prompting us to reevaluate the expression of MNDA in BPDCN.

METHODS

We collected all available BPDCN cases from the Stanford University archives collected in the past 10 years and subjected them to MNDA immunohistochemistry. In select cases, molecular profiling by next-generation sequencing was performed.

RESULTS

We found 4 cases (of 8 total examined [50%]) with convincing site-discordant MNDA expression. This expression was seen in 3 of 6 (50%) bone marrow samples, 1 of 2 (50%) breast soft tissue samples, and 3 of 14 (up to 21%) skin samples and was not obviously predicted by age, sex, history of myeloid neoplasm, or treatment history. In 2 cases, MNDA was strongly expressed in 2 distinct sites (breast/bone marrow, skin/bone marrow) and negative in subsequent samples.

CONCLUSIONS

Our findings suggest that MNDA expression in BPDCN is anatomic site dependent and transient, with noncutaneous infiltrates showing more frequent expression than cutaneous infiltrates. These results caution against the use of MNDA to exclude BPDCN when considering the differential diagnosis of a blastic extramedullary infiltrate.

PRAME expression in genital melanocytic lesions - Potential diagnostic pitfall of intermediate expression in atypical genital nevi

INTRODUCTION

The Preferentially Expressed Antigen in Melanoma (PRAME) immunostain has seen significant diagnostic use in confirming malignancy for melanocytic lesions. However, the expression of PRAME in genital melanocytic lesions have not been reported. In this study, PRAME staining was performed on a cohort of genital melanocytic lesions, aiming to investigate the diagnostic role of PRAME in genital melanocytic lesions and its expression in atypical genital nevi.

METHODOLOGY

A cohort including genital invasive melanoma, melanoma-in-situ, atypical genital nevus (AGN), compound nevus, intradermal nevus, blue nevus, lentigo and melanosis was retrieved with histology reviewed and PRAME immunostaining performed.

RESULTS

A total of 66 cases were reviewed. The average proportion expression of PRAME were 56.75 % and 57.43 % for invasive melanoma and melanoma-in-situ, with average H-scores of 153.5/300 and 163.14/300 respectively, which were greater than AGN (3.25 %, 7.75/300, p<0.001), compound/intradermal nevi, lentigo/melanosis, and background junctional melanocytes (<1 %, <1/300, p<0.001). The different cutoffs of PRAME expression, the sensitivity and specificity were 65.22 % and 100 % (>100/300); 69.57 % and 95.83 % (>10/300); and 82.61 % and 93.75 % (≥1/300) respectively. Low level PRAME expression was seen in half of the cases of AGN (n=2/4, 50 %), and at low cutoffs (>10/300 and ≥1/300) unable to differentiate invasive melanoma from AGN (p>0.05).

CONCLUSIONS

For genital melanocytic lesions, PRAME immunostain shows high specificity at strong and diffuse staining. AGN not uncommonly display low level expression. Focal and/or weak PRAME expression should not be considered as an absolute indication of malignancy, and comprehensive histological assessment remains the key to accurate diagnosis of melanocytic lesions.

Characterization of PRAME immunohistochemistry reveals lower expression in pediatric melanoma compared to adult melanoma

Pediatric melanomas are rare tumors that have clinical and histological differences from adult melanomas. In adult melanoma, the immunohistochemical marker PRAME is increasingly employed as a diagnostic adjunct. PRAME is also under investigation as a target structure for next-generation immunotherapies including T-cell engagers. Little is known about the characteristics of PRAME expression in pediatric melanoma. In this retrospective study, samples from 25 pediatric melanomas were compared with control groups of melanomas in young adults (18-30 years; n = 32), adult melanoma (>30 years, n = 30), and benign melanocytic nevi in children (0-18 years; n = 30) with regard to the immunohistochemical expression of PRAME (diffuse PRAME expression >75%/absolute expression). Pediatric melanomas show lower diffuse PRAME expression (4%) and lower absolute PRAME expression (25%) compared to young adult melanomas (15.6%/46.8%) and adult melanomas (50%/70%). A significant age-dependent expression could be observed. An analysis of event-free survival shows no prognostic role for PRAME in pediatric melanoma and young adult melanoma, but a significant association with diffuse PRAME expression in adulthood. The age dependency of PRAME expression poses a potential pitfall in the diagnostic application of melanocytic tumors in young patients and may limit therapeutic options within this age group. The immunohistochemical expression of the tumor-associated antigen PRAME is an increasingly important diagnostic marker for melanocytic tumors and is gaining attention as a possible immunotherapeutic target in melanoma. As the available data primarily stem from adult melanoma, and given the clinical and histological distinctions in pediatric melanomas, our understanding of PRAME expression in this specific patient group remains limited. The age-dependent low PRAME expression shown here constrains the use of this marker in pediatric melanoma and may also limit the use of immunotherapeutic strategies against PRAME in young patients.

Performance of preferentially expressed antigen in melanoma (PRAME) immunohistochemistry for metastatic melanoma in cytology specimens

BACKGROUND

Preferentially expressed antigen in melanoma (PRAME) has been introduced as a new melanoma marker and potential target for immunotherapy. While PRAME immunohistochemistry (IHC) is well documented in surgical pathology, similar data in cytology are limited. Metastatic melanoma is frequently diagnosed via cytology samples in which IHC plays an important role. We aimed to accordingly evaluate the performance of PRAME IHC in diagnosing metastatic melanoma in cytology samples relative to other commonly used melanoma markers.

MATERIALS AND METHODS

The study included 156 archival cytology cases, of which 93 were melanoma cases and 63 nonmelanoma cases (controls). All cases underwent PRAME IHC staining on cell blocks. Nuclear staining of PRAME was evaluated using a quantitative and qualitative scale. Other melanocytic IHC stain results (SOX10, S-100, Melan-A, and HMB45) were also documented.

RESULTS

PRAME was detected in tumor cells in 86% of melanoma cases, which was significantly lower than SOX10 (100%) (p < .01), and similar to HMB45 (84%) and Melan-A (82%). S-100 had the lowest sensitivity of 71%. In comparison to other types of melanomas, spindle cell melanoma exhibited higher negativity for PRAME IHC (4/10 = 40%). PRAME was also expressed in some nonmelanocytic malignancies including carcinoma (5/22 = 23%), sarcoma (5/15 = 33%), and hematologic malignancies (1/9 = 11%). Overall, PRAME showed a sensitivity of 86%, specificity of 82%, positive predictive value of 70%, and negative predictive value of 92% for metastatic melanoma.

CONCLUSIONS

PRAME is a useful marker for the diagnosis of melanoma in cytology material, but it is less sensitive than SOX10. PRAME is also expressed in other nonmelanocytic tumors which limits its specificity.

Analysis of PRAME immunocytochemistry in 109 acral malignant melanoma in situ

AIMS

Preferentially expressed antigen in melanoma (PRAME) recently is a reliable immunohistochemistry (IHC) marker for distinguishing melanoma from other lesions. However, there are few articles focused on PRAME use in acral malignant melanoma, the most common type in Asians. This study investigated PRAME IHC expression in a large series of acral malignant melanoma in situ to add to the body of clinical knowledge.

METHODS

PRAME IHC was performed in unequivocal cases of primary acral lentiginous melanoma in situ (ALMIS), subungual melanoma in situ (SMIS) and acral recurrent nevi as the control. PRAME tumour cell percentage positivity and intensity were expressed as categorised in a cumulative score by adding the quartile of positive tumour cells to intensity labelling. The final IHC expression was interpreted as negative (0-1), weak (2-3), moderate (4-5) or strong (6-7).

RESULTS

In 91 ALMIS patients, 32 cases (35.16%) were strong, 37 (40.66%) were moderate and 22 (24.18%) were weak. In 18 SMIS patients, strong positivity of PRAME was observed in 4 (22.22%) cases, moderate in 10 (55.56%) and weak in the remaining 4 (22.22%). No melanoma sample was negative for PRAME. By comparison, only 2 of the 40 acral recurrent nevi cases were positive.

CONCLUSIONS

Our study supports the ancillary value of PRAME for diagnosing ALMIS and SMIS with high sensitivity and specificity.

Immunohistochemistry Update in Dermatopathology and Bone and Soft Tissue Pathology

CONTEXT.—

Immunohistochemistry plays an important role in dermatopathology, particularly for melanocytic lesions and poorly differentiated malignancies. In the field of bone and soft tissue pathology, molecular methods remain the gold standard for diagnosis; however, immunohistochemistry targeting underlying molecular alterations represents a valuable screening tool, especially in areas with limited access to molecular testing.

OBJECTIVE.—

To describe the utility and limitations of new and emerging immunohistochemical stains in the diagnosis of skin, soft tissue, and bone tumors.

DATA SOURCES.—

A literature review of recently described immunohistochemical stains in the fields of dermatopathology and bone and soft tissue pathology was performed.

CONCLUSIONS.—

Immunohistochemistry is an important adjunctive tool for select entities in dermatopathology and bone and soft tissue pathology, and it provides pathologists with valuable evidence of their behavior, underlying molecular alterations, and line of differentiation. Furthermore, immunostains targeting molecular abnormalities have the potential to replace current molecular methods. Many of these recently described stains demonstrate higher sensitivity and specificity; however, limitations and pitfalls still exist, and correlation with morphologic and clinical findings remains essential for diagnosis.

Pitfalls of PRAME Immunohistochemistry in a Large Series of Melanocytic and Nonmelanocytic Lesions With Literature Review

ABSTRACT

Preferentially expressed antigen in melanoma (PRAME) immunohistochemistry is currently used to facilitate distinction of benign and malignant melanocytic proliferations. We hypothesized that evaluation of 1 institution's experience with PRAME labeling in a large number of consecutive cases might elucidate additional strengths and potential pitfalls and reveal base rates of positivity versus negativity in 1 academic practice. Pathology reports for all specimens on which PRAME labeling was performed at our institution between January 2021 and May 2022 were retrieved from our database. Eighty percent of conventional malignant melanomas were labeled diffusely positive with PRAME; there were no significant differences in mean age, sex, site, Breslow depth, ulceration status, or American Joint Committee on Cancer pathological tumor stage when comparing diffusely PRAME-positive malignant melanomas with those that lack diffuse labeling. Although no banal melanocytic nevi were labeled with PRAME, 13% of dysplastic nevi were diffusely PRAME positive, with junctional proliferations, severe atypia, male gender, and older age being associated with PRAME positivity. As some but not all ambiguous melanocytic lesions in which malignancy could not be excluded based on morphology alone were diffusely PRAME positive, PRAME's accuracy in predicting malignancy remains unclear to the authors; further study is needed to assess the precision to which PRAME immunohistochemistry can separate benign borderline lesions from their malignant counterparts. Among nonmelanocytic lesions, some poorly differentiated tumors, including atypical fibroxanthomas, can be PRAME positive. This series underscores the importance of clinicopathologic correlation and shows that diffuse PRAME positivity is highest in conventional malignant melanomas (∼80%, or 8 of 10 lesions), is seen in about half of challenging borderline lesions at our institution, and can be observed in lesions diagnosed as dysplastic nevi by our group (∼10% or 1 in 10 lesions), as well as in rare poorly differentiated malignancies.

Immunohistochemistry for PRAME in Dermatopathology

ABSTRACT

Preferentially expressed antigen in melanoma (PRAME) is a tumor-associated antigen first identified in a melanoma patient and found to be expressed in most melanomas as well as in variable levels in other malignant neoplasms of epithelial, mesenchymal, or hematolymphoid lineage. Detection of PRAME expression in formalin-fixed paraffin-embedded tissue is possible by immunohistochemistry (IHC) with commercially available monoclonal antibodies. In situ and invasive melanoma frequently show a diffuse pattern of nuclear PRAME immunoreactivity which contrasts with the infrequent and typically nondiffuse staining seen in nevi. In many challenging melanocytic tumors, results of PRAME IHC and other ancillary tests correlate well, but not always: The tests are not interchangeable. Most metastatic melanomas are positive for PRAME, whereas nodal nevi are not. Numerous studies on PRAME IHC have become available in the past few years with results supporting the value of PRAME IHC as an ancillary tool in the evaluation of melanocytic lesions and providing insights into limitations in sensitivity and specificity as well as possible pitfalls that need to be kept in mind by practicing pathologists.

Update on nail unit histopathology

Histopathologic evaluation of the nail unit is an essential component in the diagnosis of nail unit disorders. This review highlights recent updates in nail unit histopathology and discusses literature covering a wide range of nail disorders including melanoma/melanocytic lesions, squamous cell carcinoma, onychomatricoma, onychopapilloma, onychomycosis, lichen planus, and other inflammatory conditions. Herein we also discuss recent literature on nail clipping histopathology, a useful and noninvasive diagnostic tool that continues to grow in popularity and importance to both dermatologists and dermatopathologists.

PRAME expression in cutaneous melanoma does not correlate with disease-specific survival

BACKGROUND

Immunohistochemistry-based protein biomarkers can provide useful prognostic information in cutaneous melanoma. The independent prognostic value of Ki-67 has been studied with variable results. PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemistry is a useful new ancillary tool for distinguishing cutaneous nevi from melanoma; however, its prognostic value has not been well studied. We evaluated PRAME as a prognostic marker in cutaneous melanoma, compared to Ki-67.

METHODS

We analyzed the immunohistochemical expression of PRAME and Ki-67 in 165 melanocytic lesions, including 92 primary melanomas, 19 metastatic melanomas, and 54 melanocytic nevi using tissue microarrays. PRAME immunostaining was scored based on the percentage of positive nuclei: 0 <1%, 1+ 1%-25%, 2+ 26%-50%, 3+ 51%-75%, and 4+ >75%. The percentage of Ki-67-positive tumor nuclei was used to calculate the proliferation index.

RESULTS

PRAME and Ki-67 both showed significantly increased expression in melanomas compared to nevi (p < 0.0001 and p < 0.001, respectively). There was no significant difference in PRAME expression in primary versus metastatic melanomas. By contrast, the Ki-67 proliferation index was higher in metastatic melanoma than in primary melanoma (p = 0.013). Increased Ki-67 index correlated with ulceration (p < 0.001), increased Breslow depth (p = 0.001), and higher mitotic rate (p < 0.0001), whereas increased PRAME expression correlated with higher mitotic rate (p = 0.047) and Ki-67 index (p = 0.007). Increased Ki-67 index correlated with worse disease-specific survival in patients with primary melanoma (p < 0.001), but PRAME expression did not show prognostic significance in disease-specific survival (p = 0.63). In a multivariable analysis of patients with primary melanoma, tumor Breslow depth, ulceration, mitotic rate, and Ki-67 index were each independent predictors of disease-specific survival (p = 0.006, 0.02, 0.001, and 0.04, respectively); however, PRAME expression was not predictive of disease-specific survival (p = 0.64).

CONCLUSION

Ki-67 is an independent prognostic marker; although increased PRAME expression correlates with the Ki-67 proliferation index and mitotic rate, PRAME is not an independent prognostic marker for cutaneous melanoma. PRAME and Ki-67 are useful ancillary tools for distinguishing benign from malignant melanocytic lesions.

PRAME immunohistochemistry in soft tissue tumors and mimics: a study of 350 cases highlighting its imperfect specificity but potentially useful diagnostic applications

Preferentially expressed antigen in melanoma (PRAME) immunohistochemistry is currently used in pathology for the assessment of melanocytic neoplasms; however, knowledge of its expression patterns in soft tissue tumors is limited. PRAME immunohistochemistry (clone QR005) was assessed on whole tissue sections of 350 soft-tissue tumors and mimics (> 50 histotypes). PRAME immunoreactivity was evaluated as follows: 0 "negative" (0% positive cells); 1+ (1-25% positive cells); 2+ (26-50% positive cells); 3+ (51-75% positive cells), and 4+ "diffuse" (> 75% positive cells). PRAME was expressed in 111 lesions (0 benign, 6 intermediate malignancy, and 105 malignant), including fibrosarcomatous dermatofibrosarcoma protuberans (2/4, 0 diffuse), NTRK-rearranged spindle cell neoplasm (2/4, 0 diffuse), atypical fibroxanthoma (1/7, 0 diffuse), Kaposi sarcoma (1/5, 0 diffuse), myxoid liposarcoma (11/11, 9 diffuse), synovial sarcoma (11/11, 6 diffuse), intimal sarcoma (7/7, 5 diffuse), biphenotypic sinonasal sarcoma (3/3, 1 diffuse), angiosarcoma (10/15, 6 diffuse), malignant peripheral nerve sheath tumor (9/12, 4 diffuse), pleomorphic rhabdomyosarcoma (2/3, 2 diffuse), alveolar rhabdomyosarcoma (2/6, 0 diffuse), embryonal rhabdomyosarcoma (7/7, 4 diffuse), undifferentiated pleomorphic sarcoma (2/12, 1 diffuse), leiomyosarcoma (2/15, 1 diffuse), clear cell sarcoma of soft tissue (1/10, 0 diffuse), low-grade fibromyxoid sarcoma (1/5, 0 diffuse), Ewing sarcoma (2/10, 1 diffuse), CIC-rearranged sarcoma (8/8, 4 diffuse), BCOR-sarcoma (2/5, 1 diffuse), melanoma (20/20, 14 diffuse), and thoracic SMARCA4-deficient undifferentiated tumor (5/5, all diffuse). All tested cases of spindle cell lipoma, dedifferentiated/pleomorphic liposarcoma, dermatofibrosarcoma protuberans, solitary fibrous tumor, inflammatory myofibroblastic tumor, myxoinflammatory fibroblastic sarcoma, nodular fasciitis, myxofibrosarcoma, epithelioid hemangioendothelioma, atypical vascular lesion, hemangioma, lymphangioma, vascular malformation, papillary endothelial hyperplasia, GIST, gastrointestinal clear-cell sarcoma, malignant melanotic nerve sheath tumor, neurofibroma, schwannoma, granular cell tumor, alveolar soft part sarcoma, epithelioid sarcoma, extraskeletal myxoid chondrosarcoma, myoepithelioma, ossifying fibromyxoid tumor, angiomatoid fibrous histiocytoma, PEComa, dermatofibroma, pleomorphic dermal sarcoma, and chordoma were negative. PRAME shows imperfect specificity in soft-tissue pathology but may serve as a diagnostic adjunct in selected differential diagnoses that show contrasting expression patterns.

Advances in adoptive T-cell therapy for metastatic melanoma

Adoptive T cell therapy (ACT) is a fast developing, niche area of immunotherapy (IO), which is revolutionising the therapeutic landscape of solid tumour oncology, especially metastatic melanoma (MM). Identifying tumour antigens (TAs) as potential targets, the ACT response is mediated by either Tumour Infiltrating Lymphocytes (TILs) or genetically modified T cells with specific receptors - T cell receptors (TCRs) or chimeric antigen receptors (CARs) or more prospectively, natural killer (NK) cells. Clinical trials involving ACT in MM from 2006 to present have shown promising results. Yet it is not without its drawbacks which include significant auto-immune toxicity and need for pre-conditioning lymphodepletion. Although immune-modulation is underway using various combination therapies in the hope of enhancing efficacy and reducing toxicity. Our review article explores the role of ACT in MM, including the various modalities - their safety, efficacy, risks and their development in the trial and the real world setting.

PRAME Expression in Mucosal Melanoma of the Head and Neck Region

PRAME (PReferentially expressed Antigen in MElanoma), a cancer-testis antigen expressed in normal and neoplastic tissues with several functions, proved to be a useful diagnostic tool in the differential diagnosis between benign and malignant melanocytic lesions. The current study aims to perform PRAME stain on a retrospective case series of mucosal melanocytic tumors of the head and neck region to compare 3 different scores and evaluate the most reliable one in this diagnostic set. Immunohistochemical analysis for PRAME was performed in 54 benign and malignant mucosal melanocytic tumors of the head and neck region collected from 41 patients. The best-performing cutoff of PRAME-positive cells (nuclear stain) to differentiate benign and malignant mucosal melanocytic tumors of the head and neck region is that proposed by Raghavan and colleagues (<60%/≥60% of PRAME-positive cells), with 100% and 77.8% of benign lesions and malignant tumors respectively correctly identified. Applying this score, PRAME stain showed the best results (sensitivity, specificity, accuracy, and positive and negative predictive values) for the diagnosis of head and neck melanocytic tumors. However, a subset of PRAME-negative malignant tumors was identified, especially located in the palatal area (hard and soft palate). Finally, high PRAME expression (≥60%) was associated with specific sites (nasal cavity/nasal septum/turbinates nasopharynx, and the maxillary sinus), nodular histotype, and female sex.

Potential diagnostic utility of PRAME and p16 immunohistochemistry in melanocytic nevi and malignant melanoma

BACKGROUND

PRAME (PReferentially expressed Antigen in MElanoma) is a tumor-associated antigen that has been studied in various cutaneous melanocytic lesions. p16, on the other hand, has been proposed to aid in distinguishing between benign and malignant melanocytic neoplasms. Studies on the diagnostic utility of PRAME and p16 in combination in differentiating nevi from melanoma are limited. We aimed to assess the diagnostic utility of PRAME and p16 in melanocytic tumors and their role in distinguishing between malignant melanomas and melanocytic nevi.

METHODS

This is a single-center retrospective cohort analysis over a 4-year period (2017-2020). We used the pathological database of malignant melanomas (77 cases) and melanocytic nevi (51 cases) specimens from patients who underwent shave/punch biopsies or surgical excisions and evaluated immunohistochemical staining percentage positivity and intensity for PRAME and p16.

RESULTS

Most malignant melanomas showed positive/diffuse PRAME expression (89.6%); on the other hand, 96.1% of nevi did not express PRAME diffusely. p16 was expressed consistently in nevi (98.0%). However, p16 expression in malignant melanoma was infrequent in our study. PRAME had a sensitivity and specificity of 89.6% and 96.1%, respectively, for melanomas versus nevi; on the other hand, p16 had a sensitivity and specificity of 98.0% and 28.6%, respectively, for nevi versus melanoma. Also, a PRAME+/p16- melanocytic lesion is unlikely to be a nevus where most nevi were PRAME-/p16+.

CONCLUSION

In conclusion, we confirm the potential utility of PRAME and p16 for distinguishing melanocytic nevi from malignant melanomas.

Combined utility of p16 and BRAF V600E in the evaluation of spitzoid tumors: Superiority to PRAME and correlation with FISH

BACKGROUND

Spitzoid melanocytic neoplasms are diagnostically challenging; criteria for malignancy continue to evolve. The ability to predict chromosomal abnormalities with immunohistochemistry (IHC) could help select cases requiring chromosomal evaluation.

METHODS

Fluorescence in situ hybridization (FISH)-tested spitzoid neoplasms at our institution (2013-2021) were reviewed. p16, BRAF V600E, and preferentially expressed antigen in melanoma (PRAME) IHC results were correlated with FISH.

RESULTS

A total of 174 cases (1.9F:1M, median age 28 years; range, 5 months-74 years) were included; final diagnoses: Spitz nevus (11%), atypical Spitz tumor (47%), spitzoid dysplastic nevus (9%), and spitzoid melanoma (32%). Sixty (34%) were FISH positive, most commonly with absolute 6p25 gain (RREB1 > 2). Dermal mitotic count was the only clinicopathologic predictor of FISH. Among IHC-stained cases, p16 was lost in 55 of 134 cases (41%); loss correlated with FISH positive (p < 0.001, Fisher exact test). BRAF V600E (14/88, 16%) and PRAME (15/56, 27%) expression did not correlate with FISH alone (p = 0.242 and p = 0.359, respectively, Fisher exact test). When examined together, however, p16-retained/BRAF V600E-negative lesions had low FISH-positive rates (5/37, 14%; 4/37, 11% not counting isolated MYB loss); all other marker combinations had high rates (56%-75% of cases; p < 0.001).

CONCLUSIONS

p16/BRAF V600E IHC predicts FISH results. "Low-risk" lesions (p16⁺ /BRAF V600E^- ) uncommonly have meaningful FISH abnormalities (11%). PRAME may have limited utility in this setting.

PRAME is a useful marker for the differential diagnosis of melanocytic tumours and histological mimics

AIMS

Although the morphological assessment of melanoma is generally straightforward, diagnosis can be especially difficult when the significant morphological and immunohistochemical results overlap with those of benign and malignant melanocytic tumours and histological mimics. This study assessed the potential diagnostic utility of measuring PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemically in naevi, melanomas and clear cell sarcomas (CCSs) in Chinese patients.

METHODS

We examined the immunohistochemical expression of PRAME in 317 melanocytic naevi, 178 primary melanomas, 72 metastatic melanomas and 19 CCSs and compared the sensitivity and specificity of PRAME immunohistochemistry (IHC) in the differential diagnosis of melanocytic tumours and histological mimics.

RESULTS

Of the 317 melanocytic naevi, 98.1%were completely negative for PRAME; six cases showed focal PRAME immunoreactivity in a minor population of lesional melanocytes. Diffuse nuclear immunoreactivity for PRAME was found in 89.9% of primary melanomas and 93.1% of metastatic melanomas. Regarding melanoma subtypes, PRAME was expressed in 100% of superficial spreading melanomas, 100% of melanomas arise in congenital naevus, 91.4% of nodular melanomas, 87.8% of acral lentigo melanomas, 80.0% of lentigo malignant melanomas, 60.0% of Spitz melanomas, 96.2% of mucosal melanomas and 80.0% of uveal melanomas. None of the two desmoplastic melanomas expressed PRAME. Of the 19 CCS cases, 89.5% were negative for PRAME and 10.5% showed focal weak PRAME immunoreactivity in a minor population of tumour cells.

CONCLUSIONS

Our findings indicate that PRAME may be a useful marker to support a suspected diagnosis of melanoma. In addition, lack of PRAME expression is a valuable hint to CCS in a suspected case, and then molecular confirmation of the presence of EWSR1 rearrangement is necessary.

PRAME Expression in Cancer. A Systematic Immunohistochemical Study of >5800 Epithelial and Nonepithelial Tumors

Preferentially expressed antigen in melanoma (PRAME) is considered a useful marker in the differential diagnosis between malignant melanoma and its melanocytic mimics. Recently PRAME expression was documented in nonmelanocytic tumors, but much of the data are based on mRNA studies. This investigation evaluated PRAME expression in the spectrum of normal tissues and >5800 human tumors using immunohistochemistry and EP461 monoclonal antibody. In normal tissues, PRAME was expressed in the testis and proliferative endometrium. In tumors, PRAME was variably expressed in malignancies of different lineages. Among epithelial tumors, >50% of PRAME-positive lesions were found among endometrial carcinomas (82%), uterine serous carcinomas (82%), uterine carcinosarcomas (60%), ovarian clear cell carcinomas (90%), ovarian serous carcinomas (63%), adenoid cystic carcinomas (81%), seminomas (78%), thymic carcinomas (75%), and basal cell carcinomas (62%). In mesenchymal and neuroectodermal malignancies, PRAME was frequently expressed in synovial sarcoma (71%), myxoid liposarcoma (76%), neuroblastoma (61%) and metastatic melanoma (87%). Also, PRAME was consistently expressed in 4 melanomas that lacked all melanoma markers including S100 protein and SOX10 but harbored typical for melanoma BRAF or NRAS driver mutations. However, strong and diffuse PRAME immunoreactivity was seen in many types of nonmelanocytic poorly differentiated carcinomas and sarcomas. Based on this study, PRAME is a relatively unspecific immunohistochemical marker, which limits its use in diagnostic surgical pathology. However, immunohistochemistry is a reliable and unexpensive method useful in detecting PRAME-positive malignancies for potential immunotherapy.

Epithelioid Vascular Lesions: The Differential Diagnosis and Approach in Cytology and Small Biopsies

Vascular neoplasms are rare tumors with a multitude of clinical presentations and behavior, which make accurate identification and subclassification challenging on limited small biopsies. Within the spectrum of these lesions, the ones with epithelioid morphology, such as epithelioid hemangioendothelioma and epithelioid angiosarcoma, are particularly challenging given the morphologic overlap with nonvascular lesions and the limited cells due to hemodilution on sampling. Herein, we review the differential diagnosis of epithelioid vascular neoplasms, with a focus on the cytomorphology, differential diagnoses, and ancillary studies that pathologists should be aware of when evaluating small biopsies and aspirates, including novel translocations, and associated monoclonal immunohistochemistry antibodies, that can help in the diagnosis of some of these tumors. Awareness of these morphologic and ancillary study findings in these rare tumors will hopefully allow pathologists to recognize and render-specific diagnoses on limited samples of these challenging lesions.

PRAME expression in melanocytic lesions of the nail

BACKGROUND

Subungual melanoma can be diagnostically challenging. We evaluated the potential of PReferentially expressed Antigen for MElanoma (PRAME) immunoreactivity for differentiating benign from malignant nail melanocytic lesions.

METHODS

Sixty cases were identified (10 invasive melanomas, 8 melanomas in situ, 14 nevi, 12 cases of lentigo, and 16 of melanocytic activation). Percentage of PRAME-positive melanocytes was evaluated as follows: 0 no staining, 1+ 1%-25%, 2+ 26%-50%, 3+ 51%-75%, and 4+ >75%. A combined score of both percentage and intensity was also evaluated.

RESULTS

The difference in PRAME expression between malignant and benign lesions was statistically significant (p < 0.0001). The degree of PRAME expression significantly correlated with patients' age and clinical size. When based on percentage score, 61.1% of melanomas showed a 4+ score, 16.7% showed a 3+ score, 11.1% showed a 1+ score, and 11.1% was negative; 69.0% of the benign lesions was negative, 23.8% showed a 1+ score, 4.8% showed a 2+ score, and 2.4% showed a 4+ score. When the cutoff value for malignancy decreased from 4+ to 3+, the sensitivity increased from 61.1% to 77.8%, while specificity remained 97.6%. Combined score results were similar.

CONCLUSIONS

PRAME is a relatively sensitive and highly specific marker in differentiating benign from malignant nail melanocytic lesions. However, correlation with morphology is imperative.

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.

Comparative Analysis of PRAME Expression in 127 Acral and Nail Melanocytic Lesions

PRAME (PReferentially expressed Antigen in MElanoma), a cancer testis antigen expressed in low levels in gonadal, endometrial, and adrenal gland tissues, has been recently considered a valuable tool in the differential diagnosis between benign and malignant melanocytic lesions. The aim of the current study is to perform PRAME immunostaining on a large series of benign and malignant acral lesions to evaluate the reproducibility of data reported in the literature and to validate PRAME as an affordable tool in the differential diagnosis between benign and malignant acral melanocytic tumors. Immunohistochemical analysis for PRAME was performed in 127 benign and malignant acral and nail melanocytic lesions. To better correlate PRAME expression with the nature (benign vs. malignant) of the lesions, we categorized PRAME tumor cells percentage positivity and intensity in a cumulative score obtained by adding the quartile of positive tumor cells (0, 1+, 2+, 3+, 4+) to PRAME expression intensity in tumor cells (0, 1+, 2+, 3+). Adopting an arbitrary PRAME expression score of < 5 versus ≥5 resulted in a correct identification of 82.5% of benign and 87.1% of malignant lesions. PRAME immunohistochemistry demonstrated good sensitivity and specificity in the diagnosis of acral melanocytic lesions, however, in line with the previous literature, we identified a subset of challenging cases such as acral Spitz nevi, in situ melanomas, and small, thin, invasive melanomas in which PRAME did not correlate with morphologic features. This suggests that PRAME can be a valid tool to be incorporated in a diagnostic clinicopathologic algorithm, subject to morphologic characteristics.

Preferentially Expressed Antigen in Melanoma (PRAME) and Human Malignant Melanoma: A Retrospective Study

BACKGROUND

Preferentially expressed antigen in melanoma (PRAME) is a cancer testis antigen (CTA) identified in 1997 through analysis of the specificity of tumor-reactive T-cell clones derived from a patient with metastatic cutaneous melanoma. Although at first it seemed even more specific, various studies have shown that PRAME can also be expressed in the context of atypical lesions that do not correspond solely to the definition of malignant melanoma.

METHODS

A systematic review of English articles was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

126 records were identified in the literature search, of which 9 were duplicates. After screening for eligibility and inclusion criteria, 53 publications were included.

CONCLUSIONS

The advent of a new marker such as PRAME is surely a step forward not only in the diagnostic approach, but also in the immunotherapeutic approach to MM. However, various studies have shown that PRAME can also be expressed in the context of atypical lesions apart from MM and, for this reason, the diagnostic sensitivity and specificity (hence accuracy) are clearly lower. Further studies with larger case series will be necessary to understand better what possibilities are offered in terms of diagnostic reliability by PRAME.

Preferentially expressed antigen in melanoma immunohistochemistry as an adjunct for differential diagnosis in acral lentiginous melanoma and acral nevi

Preferentially expressed antigen in melanoma (PRAME) has shown promising utility in distinguishing benign melanocytic lesions from melanomas, but knowledge of its expression pattern in acral lentiginous melanoma (ALM) and acral nevi (ANs) is limited. Immunohistochemical expression of PRAME was examined in 75 ALMs and 34 ANs. The clinical and histopathologic characteristics of patients with ALM were collected. PRAME was immunoreactive in 89.3% (67/75) of ALMs, but entirely negative in 94.1% (32/34) of ANs. When staining at least 50% of lesional melanocytes was determined as positivity, the sensitivity and specificity of PRAME for distinguishing ALM from ANs were 69.3% and 100%, respectively. Seventy-one cases of ALMs had tumor cells in the epidermis; 71.8% (51/71) of them showed positive for PRAME. By contrast, 61 ALMs had tumor cells in the dermis; 65.6% (40/61) exhibited positive expression. Twenty-nine of 39 (74.4%) epithelioid cell ALMs were observed to be positive for PRAME. By comparison, 63.8% (23/36) of ALMs with spindle tumor cells were positive for PRAME. However, PRAME positive expression was not associated with any clinical and histopathologic characteristics of patients with ALM, including Breslow thickness, ulcer, cytomorphology, lymph node metastasis, or tumor-infiltrated lymphocytes (TILs). Nevertheless, we observed that 82.6% (19/23) of ALMs with lymph node involvement at diagnosis expressed PRAME, compared with 57.6% (20/35) of those without. In summary, PRAME immunohistochemistry can serve as a helpful adjunct in the differential diagnosis of ALMs and ANs with good sensitivity and high specificity. Additionally, PRAME tends to have a higher positive rate in epidermal melanocytes than in the dermis and is inclined to express in epithelioid cells than in spindle cells of ALMs.

PRAME Expression in Challenging Dermal Melanocytic Neoplasms and Soft Tissue Tumors With Melanocytic Differentiation

ABSTRACT

Preferentially expressed antigen in melanoma (PRAME) is an immunohistochemical biomarker that is diffusely expressed in most cutaneous melanomas and is negative in most benign nevi. Histologically challenging dermal melanocytic neoplasms, such as cellular blue nevi (CBN) and deep penetrating nevi (DPN), and soft tissue tumors with melanocytic differentiation, such as clear cell sarcoma and perivascular epithelioid cell tumor, may resemble primary or metastatic melanoma. PRAME immunohistochemistry (IHC) was applied to archived formalin-fixed, paraffin-embedded specimens of various dermal melanocytic neoplasms and soft tissue neoplasms with melanocytic differentiation. Staining was graded based on the percentage of melanocytes labeled (0-4+ as previously reported). The gold standard was final pathologic diagnosis using histologic, immunophenotypic, and in some cases molecular findings. Fifty-four cases were evaluated. 62.5% (5/8) of blue nevus-like melanomas and 50% (1/2) of DPN-like melanomas were PRAME positive (4+). Of the other tumors, 100% (20/20) of CBN (including 1 atypical CBN with borderline features); 100% (12/12) of DPN, combined DPN, or borderline DPN; 88.9% (8/9) of perivascular epithelioid cell tumors; and 100% (3/3) of clear cell sarcoma were PRAME negative (0-2+). Within the borderline categories specifically, all 8 tumors (1 borderline CBN and 7 borderline DPN) showed low (0-2+) PRAME expression. Overall, the sensitivity for melanoma in this context was 60%, with a specificity of 97.7%. Although our sample size is limited, the results suggest that IHC staining for PRAME may be useful in supporting a diagnosis of melanoma in the setting of challenging dermal melanocytic neoplasms and other epithelioid neoplasms with melanocytic differentiation. However, PRAME IHC lacks sensitivity in this context.

HMB45/PRAME, a Novel Double Staining for the Diagnosis of Melanocytic Neoplasms: Technical Aspects, Results, and Comparison With Other Commercially Available Staining (PRAME and Melan A/PRAME)

PRAME (PReferentially expressed Antigen in MElanoma) is a tumor-associated antigen that was recently found to be expressed by malignant melanocytic lesions but not by benign ones, thus resulting useful in this diagnostic field. PRAME could also be expressed by some normal tissues and nonmelanocytic tumors, suggesting as caution should be adopted to use PRAME as a "pan-melanoma" marker for the differential diagnosis with other malignant tumors. Until now, PRAME expression was exclusively investigated through single staining with a monoclonal antibody targeting PRAME and with double staining for Melan A/PRAME found to be useful in specific diagnostic sets. Herein, we studied the expression of PRAME in 40 melanocytic lesions and 23 nonmelanocytic ones using PRAME, Melan A/PRAME, and novel double staining for HMB45/PRAME. Although our results need to be validated, they support the adoption of HMB45/PRAME, alone or in combination with PRAME and Melan A/PRAME, as a helpful marker in the diagnosis of melanocytic neoplasms with a high concordance rate between primary melanoma and corresponding metastases.

Immunohistochemistry in melanocytic lesions: Updates with a practical review for pathologists

This review provides a summary of the immunohistochemical markers pertinent to the diagnosis of melanocytic lesions. There is considerable morphologic overlap between benign and malignant melanocytic lesions, and given the significant differences in clinical management, the diagnostic workup becomes crucial. Immunohistochemistry aids in the distinction between various melanocytic proliferations and recent contributions to the literature have furthered our optimization of panels in the diagnostic workup. In recent years, SOX10 has been considered as the optimal marker for melanocytic lesions given the similar sensitivity but higher specificity than S100. HMB-45 is less sensitive than S100 but demonstrates utility in confirmation of deceptively banal small cell and nevoid melanoma variants where deep nests of melanocytes are highlighted. Melan-A (MART-1) and MiTF show similar sensitivity to S100 however there is a lack of expression in spindle cell and desmoplastic melanomas.

Sensitive Immunofluorescent Detection of the PRAME Antigen Using a Practical Antibody Conjugation Approach

Bioconjugation of antibodies with various payloads has diverse applications across various fields, including drug delivery and targeted imaging techniques. Fluorescent immunoconjugates provide a promising tool for cancer diagnostics due to their high brightness, specificity, stability and target affinity. Fluorescent antibodies are widely used in flow cytometry for fast and sensitive identification and collection of cells expressing the target surface antigen. Nonetheless, current approaches to fluorescent labeling of antibodies most often use random modification, along with a few rather sophisticated site-specific techniques. The aim of our work was to develop a procedure for fluorescent labeling of immunoglobulin G via periodate oxidation of antibody glycans, followed by oxime ligation with fluorescent oxyamines. Here, we report a novel technique based on an in situ oxime ligation of ethoxyethylidene-protected aminooxy compounds with oxidized antibody glycans. The approach is suitable for easy modification of any immunoglobulin G, while ensuring that antigen-binding domains remain intact, thus revealing various possibilities for fluorescent probe design. The technique was used to label an antibody to PRAME, a cancer-testis protein overexpressed in a number of cancers. A 6H8 monoclonal antibody to the PRAME protein was directly modified with protected-oxyamine derivatives of fluorescein-type dyes (FAM, Alexa488, BDP-FL); the stoichiometry of the resulting conjugates was characterized spectroscopically. The immunofluorescent conjugates obtained were applied to the analysis of bone marrow samples from patients with oncohematological diseases and demonstrated high efficiency in flow cytometry quantification. The approach can be applied for the development of various immunofluorescent probes for detection of diagnostic and prognostic markers, which can be useful in anticancer therapy.

PRAME expression in cellular neurothekeoma: A study of 11 cases

BACKGROUND

Preferentially expressed antigen in melanoma (PRAME) has been widely investigated in the skin, mainly in melanocytic tumors, and constitutes an aid in differentiating benign from malignant lesions. Very few studies have been performed on non-melanocytic tumors.

MATERIALS

We investigated the immunohistochemical expression of PRAME on a series of 11 neurothekeomas (NTKs), together with 3 cases of nerve sheath myxoma (NSM) and 1 case of plexiform fibrohistiocytic tumor (PFT), in order to evaluate the presence and usefulness of this marker in their differential diagnosis.

RESULTS

PRAME was variably expressed in all cases of NTK, with moderate intensity in three cases and faint in the remaining cases; on the contrary, cases of NSM and PFT were negative.

CONCLUSIONS

This study expands the entities of cutaneous non-melanocytic tumors expressing PRAME, and confirms that this marker is not restricted to malignant tumors. Expression of PRAME in NTK does not seem to be related to distinctive histopathologic features.

Preferentially expressed antigen in melanoma and p16 expression in acral melanocytic neoplasms

Acral melanocytic neoplasms often pose diagnostic difficulty. Preferentially expressed antigen in melanoma (PRAME) expression and loss of p16 expression have diagnostic utility in melanocytic tumors. We examined PRAME and p16 expression in 30 acral melanocytic neoplasms (n = 11 nevi; n = 2 dysplastic nevi; n = 7 Spitz nevi; n = 10 acral melanomas). PRAME was scored as % positive nuclei: negative = 0%; 1% to 25% = 1+; 25% to 50% = 2+; 50% to 75% = 3+, or positive: 75% to 100% = 4+. p16 expression was defined as retained (homogeneous or checkerboard) or lost (complete or partial/regionally). PRAME expression was negative in all benign, dysplastic, and Spitz nevi. Conversely, all acral melanomas were diffusely (4+) positive for PRAME expression. p16 expression was retained in all benign acral nevi (8/11 homogeneous, 3/11 checkerboard), completely lost in one dysplastic nevus, and retained in all acral Spitz nevi (3/7 homogeneous, 4/7 checkerboard). p16 was retained in five of 10 acral melanomas (3/10 homogeneous; 2/10 checkerboard), and negative in five of 10 acral melanomas (absent in 3/10, partially lost in 2/10). Our data suggest that 4+ PRAME expression is highly sensitive and specific in the setting of acral melanomas and is a more predictive diagnostic tool compared with p16 immunohistochemistry.

The utility of PRAME immunohistochemistry in the evaluation of challenging melanocytic tumors

BACKGROUND

PRAME (PReferentially expressed Antigen in Melanoma) immunohistochemistry has demonstrated high specificity for unequivocal melanomas; however, its utility in ambiguous melanocytic neoplasms has yet to be fully elucidated.

METHODS

Cases of challenging melanocytic neoplasms were subclassified into one of three categories: challenging, favor benign (FB), challenging, cannot be subclassified (CCS), or challenging, favor malignant (FM). Using a previously published system, whereby cases with diffuse staining (>75%) were considered positive, scoring of PRAME was performed. Additionally, tumors with hotspot staining were also considered positive.

RESULTS

Sixteen out of 85 tumors showed positive staining representing 5% of FB tumors, 24% of CCS tumors, and 47% of FM. In FB and CCS tumors, positive staining was mainly encountered in atypical intraepidermal melanocytic proliferations and spitzoid neoplasms. The specificity of positive PRAME staining was 95% and its concordance with the final diagnostic interpretation was 75%.

CONCLUSIONS

PRAME positivity is more common in neoplasms favored to be malignant by histopathologic evaluation. Its clinical utility may include early diagnosis of incipient melanoma in situ. Rarely, benign melanocytic neoplasms could show diffuse expression of PRAME, and additional studies are needed to determine optimal utilization. Lastly, hotspot staining may increase its sensitivity without much compromise in specificity.

Diffuse PRAME Expression Is Highly Specific for Thin Melanomas in the Distinction from Severely Dysplastic Nevi but Does Not Distinguish Metastasizing from Non-Metastasizing Thin Melanomas

Simple Summary

Histological diagnoses within the spectrum from moderately dysplastic nevi to thin melanomas are neither accurate nor reproducible, emphasizing the need for more objective supplemental immunohistochemical markers. PRAME immunohistochemistry aids in differentiating unequivocal melanomas from unequivocal nevi. The aim of our study was to determine whether PRAME IHC also allows differentiation of severely dysplastic nevi from thin melanomas and whether PRAME is of prognostic significance in thin melanomas. We studied 70 thin melanomas, of which 35 metastasized and 35 did not metastasize and 35 severely dysplastic nevi. We found that diffuse PRAME expression was highly specific but only moderately sensitive for thin melanomas. Melanomas and severely dysplastic nevi with PRAME immunoreactivity had different staining patterns. Most Melanomas demonstrated diffuse PRAME staining of intraepidermal and dermal melanocytes while most severely dysplastic nevi showed a decreasing gradient with depth. PRAME did not allow for the differentiation of metastasizing and non-metastasizing melanomas.

Abstract

Background: PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemistry is increasingly used as diagnostic adjunct in the evaluation of melanocytic tumors. The expression and prognostic significance of PRAME in melanomas ≤1.0 mm and its diagnostic utility in the distinction from severely dysplastic compound nevi (SDN) have not been studied. Methods: We investigated and compared the immunohistochemical PRAME expression in 70 matched thin metastasizing and non-metastasizing melanomas and 45 nevi from patients with long-term follow-up (35 SDN and 10 unequivocally benign compound nevi). Results: Diffuse PRAME staining in >75% of lesional epidermal and dermal melanocytes identified 58.6% of thin melanomas but did not distinguish metastasizing from non-metastasizing melanomas (p = 0.81). A superficial atypical melanocytic proliferation of uncertain significance, in which the final diagnostic interpretation favored a SDN was the only nevus with diffuse PRAME expression (1/45). Melanomas and SDN with PRAME immunoreactivity exhibited different staining patterns. Most melanomas (67.6%) showed uniform PRAME expression in the in situ and invasive component, whereas most SDN (81.0%) showed a decreasing gradient with depth. Conclusion: Diffuse intraepidermal and dermal PRAME staining is highly specific for melanomas in the distinction from SDN. PRAME expression is not a prognostic biomarker in melanomas ≤1.0 mm.

PRAME expression in melanocytic lesions of the conjunctiva

AIMS

PRAME (PReferentially expressed Antigen in MElanoma) is a tumour-associated antigen that is preferentially strongly expressed in most cutaneous melanomas but not or only focally in nevi. Our aim was to evaluate PRAME expression in melanocytic lesions of the conjunctiva.

METHODS AND RESULTS

Surgical specimens of 114 conjunctival melanocytic nevi of different types (including 67 common, 25 combined deep penetrating and 21 inflamed juvenile nevi), 30 invasive melanomas, 10 in situ melanomas, 23 primary acquired melanoses (PAM) without atypia and 11 PAM with atypia were analysed for PRAME expression by immunohistochemistry. Nuclear positivity for PRAME in melanocytes was assessed as the percentage of positive nuclei: negative (0%), 1+ (1-25%), 2+ (26-50%), 3+ (51-75%) and 4+ (>75%). In 113 of 114 conjunctival melanocytic nevi, PRAME was either completely negative or focally 1+ positive. Diffuse 4+ PRAME expression was identified in 17 of 30 (57%) invasive melanomas, 7 of 10 (70%) in situ melanomas, 4 of 5 (80%) PAM with severe atypia, 0 of 3 PAM with moderate atypia, 0 od 3 PAM with mild atypia, 1 of 23 (4%) PAM without atypia and 0 of 114 nevi. Diffuse 4+ PRAME expression in invasive melanomas correlated with a higher mitotic count but was not related to age and gender of the patients, Breslow thickness, location or mutational status.

CONCLUSION

Diffuse 4+ PRAME positivity is highly specific for malignant conjunctival melanocytic lesions. PRAME is therefore a useful ancillary marker to support the diagnosis of a suspected conjunctival melanoma.

Diagnostic utility of PRAME in distinguishing proliferative nodules from melanoma in giant congenital melanocytic nevi

We describe a case of a melanocytic proliferation arising in a giant congenital melanocytic nevus (CMN) and outline the potential utility of an immunohistochemical study with PReferentially expressed Antigen in MElanoma (PRAME) in distinguishing benign proliferative nodules (PN) from melanoma in this context. A 15-day-old girl presented with a fibrotic nodule clinically suspicious for melanoma within a giant CMN. Histopathological examination showed a predominantly intradermal melanocytic nevus with congenital features intermixing with an ill-defined proliferation of larger melanocytes demonstrating mild-to-moderate cytologic atypia and increased mitotic activity. Anti-PRAME was diffusely positive within the congenital nevus while negative within the larger proliferating cells. Chromosomal microarray analysis revealed whole chromosomal gains and losses only, consistent with a PN arising in a giant CMN. To our knowledge, PRAME expression in giant CMN, PN, and pediatric melanomas has not been previously described. Based on our experience with this case, we propose that differential patterns of PRAME expression may be present in these three lesions, allowing PRAME immunohistochemistry to potentially serve as a helpful adjunct diagnostic tool for laboratories that do not readily have access to molecular testing in rendering a diagnosis for atypical melanocytic proliferations arising in giant CMN.

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.

Preferentially Expressed Antigen in Melanoma Immunostaining in a Series of Melanocytic Neoplasms

ABSTRACT

In their 2018 article, Lezcano et al [AJSP 2018(11):1456] show that diffuse tumor cell nuclear reactivity for Preferentially expressed Antigen in Melanoma (PRAME) is a feature of melanoma and that benign and atypical melanocytic tumors are PRAME negative or show only focal positivity for PRAME. We report our observations of PRAME staining in 253 melanocytic tumors. Tumors were classified by hematoxylin and eosin sections. The nuclear PRAME staining of neoplastic melanocytes in each case was categorized as absent, focally present, or diffusely present. The results were compared with those of Lezcano et al 105 of 134 (78%) melanocytic nevi were completely PRAME negative. Of the 29 PRAME-positive benign lesions, 28 exhibited focal but not diffuse positivity, including atypical (n = 11) and dysplastic nevi (n = 11). One of 11 Spitz nevi showed diffuse positivity (9%). Thirty-nine of 51 (76%) invasive melanomas, 41 of 50 (82%) melanoma in situ, and 15 of 18 (83%) metastatic melanomas were diffusely PRAME positive. Excluding desmoplastic melanomas, 39 of 49 (80%) primary melanomas were diffusely PRAME positive. Our findings of PRAME staining in melanocytic neoplasia are in general agreement with those of Lezcano et al. Diffuse PRAME reactivity in neoplastic melanocytes is a feature of malignancy and was only otherwise seen in 1 Spitz nevus. Caution is advised in interpretation of PRAME reactivity in melanocytic tumors of uncertain classification because melanoma arising in association with nevus and some atypical melanocytic tumors may show focal or incomplete PRAME staining. Routine histopathological findings, clinical information, PRAME staining, and judicious application of molecular studies are steps leading to accurate classification of melanocytic neoplasia.