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

PRAME and Historical Immunohistochemical Antibodies Ki-67, P16, and HMB-45 in Ambiguous Melanocytic Tumors

ABSTRACT

Ambiguous melanocytic lesions/tumors (AMLs) can be simply described as melanocytic neoplasms that cannot be differentiated as either a melanoma or a nevus. Preferentially expressed antigen in melanoma (PRAME) is a novel antibody that can help differentiate between nevi and melanomas. However, its usefulness remains controversial in AMLs. The aim of this study was to demonstrate the importance of PRAME and diagnostic auxiliary antibodies (Ki-67, p16, HMB-45) in the diagnosis of melanocytic lesions, especially in AMLs. This study included 52 ambiguous melanocytic lesions, 40 nevi, and 40 melanomas. All immunohistochemical studies were performed automatically using the Universal Alkaline Phosphatase Red Detection Kit. Different analytic approaches were used for each antibody based on the literature. Statistically, the multinomial forward stepwise elimination logistic regression analysis was used to create a statistical model to predict the diagnosis of melanocytic lesions based on clinical, morphological, and immunohistochemical data. PRAME positivity was very strong and diffuse in the melanoma group and statistically significantly higher than that of the AML and nevus groups. There was no statistically significant difference between the nevus and AML groups. The Ki-67 proliferation index and HMB-45 staining pattern provided valuable indications for distinguishing between these 3 groups. The P16 antibody was limited in supporting the differential diagnosis. Our statistical model showed that a high mitosis count, central pagetoid spread, and PRAME positivity increased the probability of melanoma against an AML diagnosis. This study showed the advantages of evaluating the PRAME antibody together with morphological features and other immunohistochemical markers (Ki-67 and HMB-45) in the differential diagnosis of melanocytic lesions.

Digital quantification of PRAME for distinguishing melanoma from nevi compared to manual assessment

AIMS

In this proof-of-concept study, we propose a new method for automated digital quantification of PRAME (PReferentially expressed Antigen of MElanoma) as a diagnostic aid to distinguish between benign and malignant melanocytic lesions. The proposed method utilizes immunohistochemical virtual double nuclear staining for PRAME and SOX10 to precisely identify the melanocytic cells of interest, which is combined with digital image analyse to quantify a PRAME-index.

METHODS

Our study included 10 compound nevi, 3 halo nevi, and 10 melanomas. Tissue slides were stained with PRAME, scanned, the cover glass removed, stained with SOX10, scanned again, and finally analysed digitally. The digitally quantified PRAME-index was compared with a manual qualitative assessment by a dermatopathologist using the standard PRAME-scoring system.

RESULTS

The digitally quantified PRAME-index showed a sensitivity of 70 % and a specificity of 100 % for separating melanomas from benign lesions. The manual qualitative PRAME-score showed a sensitivity of 60 % and a specificity of 100 %. Comparing the two methods using ROC-analyses, our digital quantitative method (AUC: 0.931, 95 % CI: 0.834;1.00, SD: 0.050) remains on par with the manual qualitative method (AUC: 0.877, 95 % CI: 0.725;1.00, SD: 0.078).

CONCLUSION

We found our novel digital quantitative method was at least as precise at classifying lesions as benign or malignant as the current manual qualitative assessment. Our method has the advantages of being operator-independent, objective, and replicable. Furthermore, our method can easily be implemented in an already digitalized pathology department. Given the small cohort size, more studies are to be done to validate our findings.

Utility of next-generation sequencing in the diagnosis of metastatic melanoma: A case report

During routine dermatologic examination, a 77-year-old male was noted to have a firm blue subcutaneous nodule on his right lateral upper back. His past medical history included metastatic melanoma of unknown primary involving right and left axillary lymph nodes, treated with ipilimumab/nivolumab with complete response, and subsequent primary uveal melanoma. The subcutaneous nodule was located near his previous right axillary scar for metastatic melanoma. Excision of the nodule showed a plexiform neoplasm involving mid and deep dermis composed of spindle and epithelioid atypical cells admixed with numerous melanophages. Central necrosis was present. Immunohistochemical studies revealed the tumor cells to be diffusely positive for HMB45, with retained expression of BAP1 and p16. The tumor cells were negative for PRAME, nuclear expression of β-catenin, LEF1, and BRAF V600E. Molecular studies demonstrated BAP1 and GNA11 somatic mutations, a profile different from that exhibited by his prior melanoma. Collectively, these data were interpreted as a metastasis from uveal melanoma and not a recurrence of his metastatic likely cutaneous melanoma after complete response to immunotherapy. This case emphasizes the importance of molecular studies for definitive diagnosis in challenging clinical situations, especially when there is discordance among histopathological, immunohistochemical, and molecular studies. Integration of clinical, histopathological, and molecular features is warranted.

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.

Renal Metastatic Melanoma Presenting With Solitary Mass

The kidney is a rare site of metastatic implantation. Metastases to the kidney most commonly originate from carcinomas in the lungs, breasts, and colon. Melanoma metastasis to the kidney is rare. We present an unusual case of melanoma metastasis to the kidney arising in a 76-year-old male who was diagnosed with melanoma two years ago. We emphasize the importance of thorough patient anamnesis when diagnosing renal cell carcinoma or urothelial carcinoma is challenging. In cases where patients with a history of melanoma present with new masses or lesions, even in atypical areas, considering melanoma metastasis in the differential diagnosis is crucial.

Compound clear cell sarcoma with EWSR1::CREM fusion

Cutaneous clear cell sarcomas may be confused with melanomas as a result of overlapping histopathology and immunohistochemical staining. We report a case of a 41-year-old woman with a purported history of acral melanoma of the great toe. Twenty-one months after excision of the primary tumor, the patient developed a groin mass, diagnosed as metastatic melanoma on excision. Five months later, a biopsy of a lung mass was reported as metastatic melanoma. The patient was referred to our institution for treatment, which prompted molecular testing on the groin metastasis by targeted next-generation sequencing. Molecular testing results revealed TP53 and TERT promoter mutations and the absence of BRAF, KRAS, and KIT mutations; it also revealed an EWSR1::CREM fusion that was confirmed by Archer FusionPlex. The alleged acral melanoma was re-reviewed, showing an invasive amelanotic spindle cell neoplasm in the dermis with neoplastic nests at the dermal-epidermal junction; the tumor cells expressed markers of melanocytic differentiation but were negative for PRAME and BRAF immunohistochemical staining. Molecular testing of the toe and lung metastasis revealed the same EWSR1::CREM fusion. In light of the molecular findings, the diagnosis was revised to a primary acral compound clear cell sarcoma with EWSR1::CREM fusion.

Cutaneous Melanoma: A Review of Multifactorial Pathogenesis, Immunohistochemistry, and Emerging Biomarkers for Early Detection and Management

Cutaneous melanoma (CM) is an increasingly significant public health concern. Due to alarming mortality rates and escalating incidence, it is crucial to understand its etiology and identify emerging biomarkers for improved diagnosis and treatment strategies. This review aims to provide a comprehensive overview of the multifactorial etiology of CM, underscore the importance of early detection, discuss the molecular mechanisms behind melanoma development and progression, and shed light on the role of the potential biomarkers in diagnosis and treatment. The pathogenesis of CM involves a complex interplay of genetic predispositions and environmental exposures, ultraviolet radiation exposure being the predominant environmental risk factor. The emergence of new biomarkers, such as novel immunohistochemical markers, gene mutation analysis, microRNA, and exosome protein expressions, holds promise for improved early detection, and prognostic and personalized therapeutic strategies.

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.

Diagnostic utility of PRAME immunohistochemistry in PEComa family of tumors and morphologic mimics with emphasis on the gynecologic tract

Perivascular epithelioid cell tumors (PEComas), rare mesenchymal tumors with myomelanocytic differentiation, can be a diagnostic challenge, often requiring a panel of immunohistochemical markers. Preferentially expressed antigen in melanoma (PRAME) is a relatively new antigen with utility in diagnosing melanomas. This study aimed to survey PRAME expression patterns in the PEComa family of tumors and morphologic mimics. Twenty cases of PEComas and 27 non-PEComas (10 leiomyosarcomas, 3 smooth muscle tumors of uncertain malignant potential [STUMPs], 11 leiomyomas, 1 uterine inflammatory myofibroblastic tumor [IMT], and 2 low-grade endometrial stromal sarcomas [LGESSs]) were stained with PRAME and compared to previously performed HMB45 and Melan-A stains, when available. Tumors showing no or barely perceptible PRAME staining at 10× were considered negative. Tumors were considered positive if there was full nuclear staining evident at 10× in at least one 10× field. Diffuse staining was defined as positivity in at least 80% of tumor nuclei. Overall, PRAME was expressed in 70% of PEComas, with diffuse positivity in 60%. However, PRAME was not specific for PEComas, with immunopositivity in the majority (70%) of uterine leiomyosarcoma cases, though negative in STUMP, leiomyoma, IMT, and LGESS cases. PRAME sensitivity was 70% and specificity was 74%, while HMB45 was more sensitive (90%) and specific (100%), but only 15% of PEComas showed diffuse staining. Melan-A staining was less common than HMB45 or PRAME, with only 18.8% sensitivity but 100% specificity. Among gynecologic PEComas, PRAME was expressed in 75% overall and enriched among malignant cases (85.7% positive). As part of an immunohistochemical panel, PRAME could be useful in the workup of PEComa cases. In the future, PRAME-specific immunotherapies may be beneficial in treating patients with malignant PEComas.

PRAME and LEF1 in Combined Deep Penetrating Nevus and Combined Blue Nevus: Utility and Pitfalls

ABSTRACT

Deep penetrating nevi (DPN), particularly those showing combined features, or combined deep penetrating nevi (CDPN), may show histopathological resemblance to blue nevus (BN) and melanoma. Preferentially Expressed Antigen in MElanoma (PRAME) is a marker that helps distinguish melanoma from benign melanocytic lesions. Lymphoid enhancer-binding factor 1 (LEF1) has been proposed to be used in conjunction with β-catenin for diagnosis of DPN. The immunohistochemical expression of PRAME and LEF1 was evaluated in 10 DPN (including 6 CDPN and 2 DPN-like proliferations with atypical features), 16 BN (including combined and cellular BN), and 2 melanomas with features of DPN or BN. PRAME was negative in most DPN (n = 10/10, n = 9/10, one case with discrepancy between readers) and all BN (n = 16/16), while the 2 melanomas included were positive (n = 2/2). All DPN were positive for LEF1 (n = 9/9) while only a subset of BN were positive (n = 6/16, P = 0.0028; n = 5/16, P = 0.001, per both readers). LEF1 seemed to be easier to interpret than β-catenin because of its nuclear pattern of expression. The expression of LEF1 in the regular nevus component of combined BN presents a potential pitfall in practice because it may lead to misinterpretation of LEF1 as positive in the BN component of the lesion. However, a subset (approximately one-third) of combined BN seemed to show true LEF1 expression. Taking into account pitfalls in interpretation, the combinatorial panel of PRAME and LEF1, in addition to conventional histopathological features, may be useful to distinguish CDPN from combined BN and other benign and malignant mimics.

Primary Undifferentiated/Dedifferentiated Cutaneous Melanomas-A Review on Histological, Immunohistochemical, and Molecular Features with Emphasis on Prognosis and Treatment

Diagnosing cutaneous melanoma is usually straightforward based on these malignancies' histopathological and immunohistochemical features. Nevertheless, melanomas can imitate various other neoplasms, sometimes lacking the expression of conventional melanocytic markers and expressing non-melanocytic ones. Furthermore, divergent differentiation is more often encountered in metastatic melanomas and is still poorly described in primary cutaneous melanomas, and little is known about these patients' prognosis and therapeutic approach. Therefore, we reviewed the literature on undifferentiated/dedifferentiated cutaneous melanomas, and we discuss the histological, immunohistochemical, and molecular profiles of undifferentiated/dedifferentiated cutaneous melanomas to understand these peculiar lesions better and improve their diagnostic algorithm. In addition to this, we also discuss how different genetic mutations may influence prognosis and become potential therapeutic targets.

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.

Metastatic melanoma and rare melanoma variants: a review

The histopathological diagnosis of melanoma is fraught with potential pitfalls. In the setting of cutaneous metastatic melanoma, it is important to recognise the various histological patterns that can be encountered from the more common to the rare, including epidermotropic, folliculotropic, naevoid, and blue naevus-like. In addition, melanoma is notorious for phenotypic plasticity. Thus, there are many different subtypes and cytomorphological variations that can be difficult to recognise as melanoma, particularly in the recurrent or metastatic setting. Select melanoma variants including primary dermal, clear cell, plasmacytoid, signet ring cell, small cell, myxoid, rhabdoid, and dedifferentiated melanoma will be discussed, in addition to composite melanocytic neoplasms. This review is intended to remind the practitioner of key concepts of metastatic disease and select rare melanoma variants, while providing practical guidelines for accurate diagnosis.

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.

Primary Cutaneous Malignant Perivascular Epithelioïd Cell Tumor (PEComa): Case Report With Review of the Literature

Perivascular epithelioïd cell tumor (PEComa) is a mesenchymal neoplasm with epithelioïd or spindled morphology with numerous thin-walled capillaries between tumor cells. They co-express markers of both melanocytic and smooth muscle differentiation. PEComas are rare, presenting in numerous anatomic sites including lung, kidney, liver, genitourinary tract, soft tissue, and skin. Primary cutaneous PEComas are very rare entity, and malignant ones are even more uncommon. Herein, we report the case of a 92-year-old female which was presenting with 7 cm exophytic, ulcerated, hemorrhagic nodular tumor, and rapidly growing for 8 months over the right thigh. On histologic examination, we found a dermal neoplasm formed by an atypical clear cell tumor with numerous branching capillaries between tumor cells. The mitotic count was found 6 mitotic figures/10 HPF. On immunohistochemistry, tumor cells co-expressed smooth muscle and melanocytic markers, CD10, and CD68. Based on these findings, the diagnosis of primary cutaneous malignant perivascular epithelioïd cell tumor (PEComa) was made. The large size (7 cm), the count of mitoses (6 mitotic figures/10 HPF), and the nuclear pleomorphism argued for malignancy. The absence of soft tissue or visceral localization argued for the cutaneous primitive origin. Adjuvant radiotherapy and targeted therapy with mTOR inhibitor (nab-sirolimus) was indicated. To the best of our knowledge, this is only the eighth case of a primary cutaneous malignant PEComa reported in the literature to date.

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.

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.