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

PRAME Updated: Diagnostic, Prognostic, and Therapeutic Role in Skin Cancer

Preferentially Expressed Antigen in Melanoma (PRAME), a member of the cancer/testis antigen family, is central to the field of skin cancer diagnostics and therapeutics. As a nuclear receptor and transcriptional regulator, PRAME plays a critical role in inhibiting retinoic acid signalling, which is essential for cell differentiation and proliferation. Its aberrant overexpression in various malignancies, particularly cutaneous melanoma, is associated with more aggressive tumour phenotypes, positioning PRAME as both a diagnostic and prognostic marker. In melanoma, PRAME is typically highly expressed, in contrast to its weak or absent expression in benign nevi, thereby improving the accuracy of differential diagnoses. The diagnostic value of PRAME extends to various lesions. It is significantly expressed in uveal melanoma, correlating to an increased risk of metastasis. In acral melanomas, especially those with histopathological ambiguity, PRAME helps to improve diagnostic accuracy. However, its expression in spitzoid and ungual melanocytic lesions is inconsistent and requires a comprehensive approach for an accurate assessment. In soft tissue sarcomas, PRAME may be particularly helpful in differentiating melanoma from clear cell sarcoma, an important distinction due to their similar histological appearance but different treatment approaches and prognosis, or in detecting dedifferentiated and undifferentiated melanomas. In non-melanoma skin cancers such as basal cell carcinoma, squamous cell carcinoma, and Merkel cell carcinoma, the variable expression of PRAME can lead to diagnostic complexity. Despite these challenges, the potential of PRAME as a therapeutic target in melanoma is significant. Emerging immunotherapies, including T-cell-based therapies and vaccines targeting PRAME, are being investigated to exploit its cancer-specific expression. Ongoing research into the molecular role and mechanism of action of PRAME in skin cancer continues to open new avenues in both diagnostics and therapeutics, with the potential to transform the management of melanoma and related skin cancers.

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.

Refining the application of PRAME-a useful marker in high CSD and acral melanoma subtypes

Pathologic discordance affecting patient management may approach 20% in melanocytic cases following specialist review. The diagnostic utility of PRAME has been highlighted in several studies but interpretative challenges exist including its use in severely dysplastic compound nevi showing progression to melanoma in situ, nevoid melanoma, and coexisting nevi with melanoma. We examine the PRAME status of a broad spectrum of melanocytic lesions including challenging, dysplastic nevi with severe atypia from a large Irish patient cohort. Retrospective review of the dermatopathology database was conducted to evaluate the PRAME staining characteristics of two hundred and twenty-one melanocytic lesions using a commercially available PRAME antibody (EPR20330). The proportion of nuclear labeling and intensity of staining was recorded. The sensitivity and specificity of PRAME for in situ and malignant melanocytic lesions was 77% and 100%, respectively. Virtually all of our melanoma in situ from high-cumulative sun damaged (CSD) skin (22/23) and all acral lentiginous melanoma (5/5) were PRAME positive while 80% (8/10) of our lentigo maligna melanoma showed diffuse expression. None of our benign subgroup showed diffuse immunoexpression (0/82), including thirty-seven moderate or severely dysplastic nevi. In all cases of melanoma in situ arising in association with a dysplastic compound nevus (0/10), no immunoexpression was observed in the nevic component while in five cases of melanoma in situ with coexistent, intradermal nevus immunostaining was confined to the in situ component. A total of 100% (2/2) of desmoplastic melanomas and 50% (4/8) of nodular melanomas were PRAME positive. PRAME is a sensitive and highly specific immunostain in the diagnosis of in situ and invasive melanoma and we emphasize its application in the evaluation of high CSD and acral melanoma subtypes as well as in challenging threshold cases.

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.

PRAME expression in 137 primary cutaneous melanomas and comparison with 38 related metastases

Melanocytic lesions have always represented a diagnostic challenge for surgical pathologists. According to the literature, PRAME showed great promise as an immunohistochemical tool in the distinction between benign and malignant melanocytic lesions. In the present study, we retrospectively analyzed 137 thicker (Breslow > 1 mm) primary cutaneous melanomas with the aim to better understand the utility of PRAME immunohistochemistry in daily practice and also to investigate if PRAME could represent a prognostic biomarker for cutaneous melanomas. PRAME immunohistochemistry was performed in all melanomas and in the metastases with antibodies to PRAME (dilution 1:1000, clone Ab219650) on an automated immunostainer (Ventana Benchmark Ultra) using a brown chromogen (DAB). We found that melanomas (59.1%) show diffuse PRAME expression (score 4 +). 99 (72.3%) primary cutaneous melanoma had no relapse during the follow-up. Of this group of melanomas, 61/99 (61.6%) were diffusely positive for PRAME. 38 (27.7%) primary cutaneous melanoma had relapses. Of this group, 28/36 (77.7%) were diffusely positive. We did not find any statistical correlation between diffuse PRAME expression and the presence of driver mutation in BRAF gene (p = 0.927), NRAS gene (p = 0.496) or either of the two (p = 0.138). We did not find a prognostic significance of diffuse PRAME expression for relapse (p = 0.462) or survival rate (p = 0.245). The prognostic value of PRAME has been only reported in mucosal, uveal and cutaneous thin melanomas. Here, we show statistical analyses on PRAME expression for melanoma with Breslow > 1 mm based on survival rate and long-term follow-up. According to our results, PRAME is a useful immunohistochemical ancillary tool in daily practice diagnosis of melanocytic lesions.

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.

Diagnostic test accuracy meta-analysis of PRAME in distinguishing primary cutaneous melanomas from benign melanocytic lesions

PRAME is a novel immunohistochemical marker that aids the diagnosis of melanocytic lesions. Diffuse PRAME positivity suggests melanoma, whereas benign naevi are negative or only weakly positive. However, the factual diagnostic accuracy of PRAME is not well established. Moreover, some studies have suggested that the threshold of 3+/50% positive cells may be more useful in practice than the most widely used cut-off (4+/75% of positive cells). Hence, we performed a systematic review and diagnostic accuracy meta-analysis to evaluate sensitivity, specificity, likelihood ratios and optimal threshold for PRAME in distinguishing benign melanocytic proliferations from melanomas. Twenty-six studies were enrolled into the meta-analysis. A total of 2915 melanocytic lesions were analysed. The optimal threshold for PRAME positivity was estimated at 3.11, which translates into 3+ in practice. Sensitivity and specificity calculated from SROC at the 3+ threshold were 0.735 (0.631-0.818) and 0.915 (0.834-0.958), respectively, compared to 0.679 (0.559-0.957) and 0.957 (0.908-0.981) at the 4+ cut-off. In subgroup analysis, the spitzoid subgroup was characterised by the lowest sensitivity and diagnostic odds ratio of PRAME. Our findings indicate that PRAME immunohistochemistry may serve as an ancillary marker to support the diagnosis of melanoma. Nevertheless, the accuracy of PRAME may be lower in spitzoid neoplasms. Our meta-analysis suggests that the 3+/50% threshold might be more useful in practice than the 4+/75% cut-off, as it shows higher sensitivity with retained satisfactory specificity.

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.

Performance of PRAME immunohistochemistry compared with that of c-Kit, c-Myc, or cyclin D1 for the diagnosis of acral melanocytic tumors

The diagnostic role of preferentially expressed antigen in melanoma (PRAME) immunohistochemistry has not been thoroughly evaluated for acral melanocytic tumors. The objective of this study was to evaluate the utility of this modality for the diagnosis of acral melanocytic tumors compared with other potential markers. Melanocytic tumors were classified as either acral nevi, challenging melanocytic tumors (superficial atypical melanocytic proliferation of uncertain significance (SAMPUS)-favor benign (SAMPUS-FB), SAMPUS-favor malignant (SAMPUS-FM)) or acral melanomas. A total of 106 acral melanocytic tumors including acral nevi (n = 32), SAMPUS-FB (n = 17), SAMPUS-FM (n = 20), and acral melanomas (n = 37) were included. Diagnostic power, assessed using an area under the receiver operating characteristic curve (AUC) for distinguishing acral melanomas and acral nevi, was highest for PRAME (AUC = 0.997), followed by c-Myc (AUC = 0.755), cyclin D1 (AUC = 0.652), and c-Kit (AUC = 0.573). At a PRAME expression level ≥30% as a positive test for acral melanoma, the sensitivity and specificity of this marker for discriminating acral melanoma from acral nevus were 100% and 96.9%, respectively. PRAME immunohistochemistry also discriminated SAMPUS-FM from SAMPUS-FB with a sensitivity and specificity of 90.0% and 76.5%, respectively. In conclusion, PRAME immunohistochemistry can be used effectively to distinguish between various spectra of acral melanocytic neoplasms.

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 spindle cell melanoma, malignant peripheral nerve sheath tumour, and other cutaneous sarcomatoid neoplasms: a comparative analysis

Diagnosis of spindle cell/sarcomatoid melanoma may be challenging due to frequent loss of expression of melanocytic marker(s) and histomorphologic resemblance to various mesenchymal tumours, particularly malignant peripheral nerve sheath tumour (MPNST). Overexpression of PReferentially expressed Antigen in MElanoma (PRAME) supports a diagnosis of melanoma when evaluating challenging melanocytic tumours. PRAME expression in MPNST and other cutaneous sarcomatoid neoplasms, however, has not been well characterised. We aimed to determine the utility of PRAME immunostain in distinguishing spindle cell melanoma from MPNST and other sarcomatoid mimics. PRAME expression was scored by extent (0 to 4+) and intensity (0 to 3) of staining. A strong positive correlation was observed between the extent and intensity scores (r = 0.84). An extent score of 4+, defined by staining in 76-100% of tumour cells, was seen in 56% (23/41) of spindle cell melanomas, 18% (7/38) of MPNSTs, 15% (4/27) of cutaneous sarcomatoid squamous cell carcinomas (SCCs), 33% (5/15) of poorly differentiated cutaneous angiosarcomas, 12% (4/33) of atypical fibroxanthomas (AFXs), 4% (1/25) of pleomorphic dermal sarcomas (PDSs), and none (0/16) of the high-grade cutaneous leiomyosarcomas. A significant difference was found between spindle cell melanoma and all other examined sarcomatoid neoplasms except angiosarcoma. While diffuse (and often strong) PRAME expression is more frequently observed in spindle cell melanoma than MPNST, sarcomatoid SCC, AFX, PDS, and high-grade leiomyosarcoma, its limited sensitivity and specificity caution against its use as a standalone diagnostic marker. PRAME may complement other epigenetic or lineage-specific markers and should only be used as part of an immunohistochemical panel when evaluating these sarcomatoid neoplasms.

Diagnostic utility of PRAME expression by immunohistochemistry in subungual and non-subungual acral melanocytic lesions

BACKGROUND

The immunohistochemical (IHC) marker PReferentially expressed Antigen in MElanoma (PRAME) has shown promise in the diagnosis of melanocytic lesions. A few studies have investigated PRAME IHC expression in acral melanomas, but PRAME expression in subungual melanomas is largely unknown. We evaluated the utility of PRAME IHC expression in distinguishing subungual melanomas (SUM) and non-subungual acral melanomas (AM) from acral nevi (AN).

METHODS

Twenty-two SUM, 20 AM, and 14 AN were identified. IHC studies were performed using an anti-PRAME antibody. The percentage of lesional cells with PRAME expression was recorded and categorized as follows: 0%, 0; 1%-25%, 1+; 26%-50%, 2+; 51%-75%, 3+; and >75%, 4+. Patient demographics and other relevant clinicopathologic parameters were recorded.

RESULTS

Diffuse (4+) PRAME IHC expression was identified in 55% (12/22) SUM and 70% (14/20) AM, respectively. Any PRAME expression (1+ to 4+) was identified in 73% (16/22) SUMs and 95% (19/20) AM, respectively. One of 14 (7%) AN exhibited PRAME expression; interestingly, the pattern of expression was diffuse.

CONCLUSIONS

In our study, PRAME IHC expression was useful in identifying AM, including SUM. However, there are exceptions of PRAME-negative melanomas and PRAME-positive nevi.

Acral Melanocytic Neoplasms: A Comprehensive Review of Acral Nevus and Acral Melanoma in Asian Perspective

Acral melanocytic neoplasms, including acral melanocytic nevus and acral melanoma, are common melanocytic lesions in Asian populations. Both lesions occur on the volar surface of the hands and feet, and on nail units. Acral melanocytic nevi occur on the arch area of the sole, whereas acral melanomas frequently occur on weight-bearing areas of the sole, and on the fingernails. Therefore, the development of acral melanoma may be associated with chronic pressure, physical stress, or trauma. Dermoscopy is a useful adjunctive diagnostic tool for differential diagnosis. Acral melanocytic nevus is characterized by a parallel furrow pattern, whereas acral melanoma has a parallel ridge pattern. Genetic alterations are also different between the two types of lesion. BRAF and NRAS mutations are common in acral melanocytic nevus, whereas acral melanoma shows lower rates of KIT, NF1, BRAF, and NRAS mutations and remarkable copy number variations in genes such as CCND1, CDK4, hTERT, PAK1, and GAB2. Sentinel lymph node biopsy is important for staging and prognosis. Contemporary treatments for melanoma include targeted therapy for mutations and immunotherapy, such as anti-PD1 inhibitors.

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.

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.