Immunohistochemistry for PRAME in Dermatopathology

Cutaneous melanoma

Cutaneous melanoma is a common cancer in Australia and New Zealand, Europe, and North America, and its incidence is still increasing in many regions. Ultraviolet (UV) radiation exposure (for example, through excessive sunlight exposure) remains the primary risk factor for melanoma; however, public awareness campaigns have led to a marked reduction in mortality. In addition to genetic damage from UV radiation, specific genetic alterations have been linked to melanoma. The stage of the tumour at the time of diagnosis is of greater importance for melanoma prognosis than in almost any other cancer. Context-dependent genetic mutations that attenuate tumour-suppressive mechanisms or activate growth-promoting signalling pathways are crucial factors in the development of cutaneous melanoma. In addition to external factors such as UV radiation, the tumour microenvironment can contribute to melanoma progression, invasion and metastasis. Cutaneous melanoma treatment has improved considerably over the past decade with the discovery and development of immune checkpoint inhibitors and therapy targeting BRAF and MEK. Over the next decade, several priorities are likely to influence melanoma research and management, including the continued advance of precision medicine methods to identify the most suitable patients for the most effective treatment, with the aim of improving clinical outcomes.

Digital quantification of Ki67 and PRAME in challenging melanocytic lesions - A novel diagnostic tool

The interpretation of immunohistochemical markers in melanocytic lesions possesses difficulties due to expression in non-melanocytic cells and the time-consuming, non-reproducible nature of manual assessment. A digital tool that accurately quantifies Ki67 and PRAME may valuably aid pathologists in the diagnostic classification of melanocytic lesions. The aim of this study was to assess the diagnostic performance of digitally quantified Ki67 and PRAME in challenging melanocytic lesions utilizing double nuclear staining methods for accurate identification of melanocytic cells. We explored the difference in Ki67 and PRAME expression by WHO-lesion-groups and Melanocytic Pathology Assessment Tool and Hierarchy for Diagnosis version 2.0 (MPATH-Dx V2.0). Tissue slides from a cohort of 156 melanocytic lesions were stained with the Ki67/SOX10 double nuclear stain and the PRAME/SOX10 virtual double nuclear stain. Melanocytic cell specific Ki67/SOX10- and PRAME/SOX10-indexes were quantified by AI-driven digital image analysis (DIA) and compared to non-specific Ki67- and PRAME-indexes. The results showed that ROC AUC of the Ki67/SOX10-index was increased compared to the non-specific Ki67-index (p < 0.001), as opposed to the AUC of the PRAME/SOX10-index compared to non-specific PRAME-index (p = 0.090). The medians of digitally quantified Ki67- and PRAME-indexes differed significantly for the overall WHO-groups and MPATH-Dx V2.0 classes (p < 0.001). In conclusion, we found that double nuclear staining improved the diagnostic performance of Ki67, but not PRAME. The combination of digitally quantified Ki67- and PRAME-indexes may potentially serve as a tool for diagnostic classification of challenging melanocytic lesions. The proposed diagnostic tool presents the results visually, graphically, and quantitatively to optimally aid the pathologist.

PRAME Expression in Melanoma is Negatively Regulated by TET2-Mediated DNA Hydroxymethylation

Preferentially expressed Antigen in Melanoma (PRAME) and Ten-Eleven Translocation (TET) dioxygenase-mediated 5-hydroxymethylcytosine (5hmC) are emerging melanoma biomarkers. We observed an inverse correlation between PRAME expression and 5hmC levels in benign nevi, melanoma in situ, primary invasive melanoma, and metastatic melanomas via immunohistochemistry and multiplex immunofluorescence: nevi exhibited high 5hmC and low PRAME, whereas melanomas showed the opposite pattern. Single-cell multiplex imaging of melanoma precursors revealed that diminished 5hmC coincides with PRAME upregulation in premalignant cells. Analysis of The Cancer Genome Atlas and Genotype-Tissue Expression databases confirmed a negative relationship between TET2 and PRAME messenger RNA expression in melanoma. Additionally, 5hmC levels were reduced at the PRAME 5' promoter in melanoma compared with nevi, suggesting a role for 5hmC in PRAME transcription. Restoring 5hmC levels via TET2 overexpression notably reduced PRAME expression in melanoma cell lines. These findings establish a function of TET2-mediated DNA hydroxymethylation in regulating PRAME expression and demonstrate epigenetic reprogramming as pivotal in melanoma tumorigenesis.

Utilizing PRAME Expression and a Meta-Analytic Framework for iSALT to Explore Atypical Late-Onset Nevi of the Elderly and Their Relationship With Lentiginous and Nested Nevoid Melanomas

BACKGROUND

In contrast to early-onset dysplastic nevi, late-onset atypical nevi of the elderly are more often precursors to distinctive nevoid melanomas. PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemistry was applied to delineate the nevoid aspect of late-onset oncogenic nevoid pathway. Inducible Skin-Associated Lymphoid Tissue, regulatory T-cell mesenchymal hubs, has emerged as a translational tool and was used to define nevoid oncogenesis within a dynamic meta-analytic pathway.

METHODS

PRAME immunohistochemistry was applied after designating a histopathologic diagnosis. Late-onset atypical nested lentiginous nevus, lentiginous nested melanoma, and hypercellular nested nevoid melanoma were the diagnostic categories. A positive PRAME for melanoma was set at 75% percentage labeling.A wide-ranging published evidence-based database was incorporated to develop a meta-analytic framework for oncogenic nevogenesis. This combined inducible Skin-Associated Lymphoid Tissue incorporating the pleiotropic functions of regulatory T cells regulating immunity and gene regulatory epigenetics as principal modulators.

RESULTS

Concordant-negative PRAME expression was present in 64 of 81 (79%) atypical nested lentiginous nevi, concordant-positive PRAME expression occurred in 54 of 75 (72%) nevoid lentiginous and nested melanomas, and 18 of 23 (78%) nevoid hypercellular nested melanomas.

CONCLUSIONS

PRAME expression confirmed the existence of a late-onset oncogenic nevoid pathway that can be defined by histopathology. Subsequent meta-analysis data linked to the meta-analytic framework revealed that PRAME is an epigenetic surrogate antigen expressed because of repression of retinoic acid receptor signaling, preventing ligand-induced retinoic acid cellular differentiation, growth arrest, and apoptosis, and promoting melanoma growth and survival for melanomas. PRAME is only a single antigen within a highly complex dynamic framework that governs nevoid oncogenesis. Significantly, the retinoic acid/retinoic acid receptor complex has been shown to modulate the immunosuppressive arm of regulatory T cells underpinning immune tolerance and is pertinent to the broad framework but is not linked to PRAME expression in this arm.

A comprehensive review of PRAME and BAP1 in melanoma: Genomic instability and immunotherapy targets

In a thorough review of the literature, the complex roles of PRAME (preferentially expressed Antigen of Melanoma) and BAP1 (BRCA1-associated protein 1) have been investigated in uveal melanoma (UM) and cutaneous melanoma. High PRAME expression in UM is associated with poor outcomes and correlated with extraocular extension and chromosome 8q alterations. BAP1 mutations in the UM indicate genomic instability and a poor prognosis. Combining PRAME and BAP1 immunohistochemical staining facilitates effective risk stratification. Mechanistically, both genes are associated with genomic instability, making them promising targets for cancer immunotherapy. Hypomethylation of PRAME, specifically in its promoter regions, is critical for UM progression and contributes to epigenetic reprogramming. Additionally, miR-211 regulation is crucial in melanoma and has therapeutic potential. The way PRAME changes signaling pathways provides clues about the cause of cancer due to genomic instability related to modifications in DNA repair. Inhibition of poly(ADP-ribose) polymerase-1 (PARP-1) and PARP-2 in cells expressing PRAME could lead to potential therapeutic applications. Pathway enrichment analysis underscores the significance of PRAME and BAP1 in melanoma pathogenesis.

Appropriate Statistical Methods to Assess Cross-study Diagnostic 23-Gene Expression Profile Test Performance for Cutaneous Melanocytic Neoplasms

ABSTRACT

Comparing studies of molecular ancillary diagnostic tests for difficult-to-diagnose cutaneous melanocytic neoplasms presents a methodological challenge, given the disparate ways accuracy metrics are calculated. A recent report by Boothby-Shoemaker et al investigating the real-world accuracy of the 23-gene expression profile (23-GEP) test highlights this methodological difficulty, reporting lower accuracy than previously observed. However, their calculation method-with indeterminate test results defined as either false positive or false negative-was different than those used in previous studies. We corrected for these differences and recalculated their reported accuracy metrics in the same manner as the previous studies to enable appropriate comparison with previously published reports. This corrected analysis showed a sensitivity of 92.1% (95% confidence interval [CI], 82.1%-100%) and specificity of 94.4% (91.6%-96.9%). We then compared these results directly to previous studies with >25 benign and >25 malignant cases with outcomes and/or concordant histopathological diagnosis by ≥3 dermatopathologists. All studies assessed had enrollment imbalances of benign versus malignant patients (0.8-7.0 ratio), so balanced cohorts were resampled according to the lowest common denominator to calculate point estimates and CIs for accuracy metrics. Overall, we found no statistically significant differences in the ranges of 23-GEP sensitivity, 90.4%-96.3% (95% CI, 80.8%-100%), specificity, 87.3%-96.2% (78.2%-100%), positive predictive value, 88.5%-96.1% (81.5%-100%), or negative predictive value, 91.1%-96.3% (83.6%-100%) between previous studies and the cohort from Boothby-Shoemaker et al with this unified methodological approach. Rigorous standardization of calculation methods is necessary when the goal is direct cross-study comparability.

The Utilization of PRAME in the Diagnosis, Prognosis, and Treatment of Melanoma

Melanoma, a deadly form of skin cancer, has seen improved survival rates due to advances in diagnosis and treatment, yet the need for further improvement remains critical. Tumor-associated antigens, such as PRAME (Preferentially Expressed Antigen in Melanoma), offer promising avenues for enhanced diagnostic precision, prognostic assessment, and targeted immunotherapy. PRAME, a cancer testis antigen, is selectively expressed in various cancers, including melanoma, and plays a key role in promoting tumorigenesis through inhibition of retinoic acid signaling, epithelial-to-mesenchymal transition, and immune evasion. This review explores the diagnostic utility of PRAME in distinguishing melanoma from benign nevi, its prognostic value in aggressive melanoma subtypes, and its potential as a therapeutic target in cancer vaccines and adoptive T-cell therapies. While PRAME-targeted therapies face challenges such as tumor heterogeneity and immune suppression, ongoing research aims to overcome these barriers, offering hope for more effective melanoma treatments.

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.

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.

A Narrative Review of the Evolution of Diagnostic Techniques and Treatment Strategies for Acral Lentiginous Melanoma

Acral melanoma (AM) is a subtype of cutaneous melanoma located on the palms, soles, and nails. The pathogenesis of AM involves mechanical stimulation and characteristic tumor-promoting mutations, such as those in the KIT proto-oncogene. Dermoscopy is useful for diagnosing AM, which is characterized by parallel ridge patterns and irregular diffuse pigmentation. Although histopathological confirmation is the gold standard for diagnosing AM, lesions showing minimal histopathological changes should be considered early-stage AM if they clinically resemble it. Recently, immunohistochemical staining of preferentially expressed antigen in melanoma has been recognized as a useful method to distinguish benign from malignant melanocytic tumors. Research reveals that AM is associated with an immunosuppressive microenvironment characterized by increased numbers of M2 macrophages and regulatory T cells, alongside a decreased number of tumor-infiltrating lymphocytes. Mohs micrographic surgery or digit-sparing wide local excision has been explored to improve quality of life and replace wide local excision or proximal amputation. AM has a worse prognosis than other subtypes, even in the early stages, indicating its inherent aggressiveness.

PRAME expression in melanoma is negatively regulated by TET2-mediated DNA hydroxymethylation

Preferentially Expressed Antigen in Melanoma (PRAME) and Ten-Eleven Translocation (TET) dioxygenase-mediated 5-hydroxymethylcytosine (5hmC) are emerging melanoma biomarkers. We observed an inverse correlation between PRAME expression and 5hmC levels in benign nevi, melanoma in situ, primary invasive melanoma, and metastatic melanomas via immunohistochemistry and multiplex immunofluorescence: nevi exhibited high 5hmC and low PRAME, whereas melanomas showed the opposite pattern. Single-cell multiplex imaging of melanoma precursors revealed that diminished 5hmC coincides with PRAME upregulation in premalignant cells. Analysis of TCGA and GTEx databases confirmed a negative relationship between TET2 and PRAME mRNA expression in melanoma. Additionally, 5hmC levels were reduced at the PRAME 5' promoter in melanoma compared to nevi, suggesting a role for 5hmC in PRAME transcription. Restoring 5hmC levels via TET2 overexpression notably reduced PRAME expression in melanoma cell lines. These findings establish a function of TET2-mediated DNA hydroxymethylation in regulating PRAME expression and demonstrate epigenetic reprogramming as pivotal in melanoma tumorigenesis.

Teaser

Melanoma biomarker PRAME expression is negatively regulated epigenetically by TET2-mediated DNA hydroxymethylation.

The Expression of PRAME as an Aid for Diagnosis and Evaluation of Histologic Margins of Intraepidermal Cutaneous Melanoma in Xeroderma Pigmentosum Patients

Xeroderma Pigmentosum (XP) is a genetic disorder characterized by photosensitivity, dyschromia, and high risk of skin cancer. From a clinical and histologic view, it can be difficult to diagnose cutaneous melanoma (CM) in XP patients and to define its resection margins. We aimed to study the role of PRAME (PReferentially Expressed Antigen in MElanoma) in differentiating intraepidermal CM from superficial atypical melanocytic proliferation of uncertain significance (SAMPUS) and evaluating the histological margins of CMs. We included XP patients. melanocitic and nonmelanocytic lesions with adjacent skin, and, as control groups, sun-damaged skin from non-XP individuals. Melanocytic lesions with a consensus diagnosis were grouped into CM, SAMPUS, or benign. The selected samples were PRAME-immunoshistochemically stained, and the ratio between immuno-positive cells/mm was recorded, according to Olds and colleagues for intraepidermal lesions. Lezcano and colleagues' method was used for intradermal lesions. Clinical data from XP patients were reviewed. All 9 patients were alive and well at the study closure, even those who developed melanoma metastases. Positive/diffuse PRAME expression was found in 29% (7/24) of intraepidermal CMs and 20% (1/5) SAMPUS samples. All 103 XP control samples and 24 adjacent lesions skin of non-XP patients were PRAME negative. This was a single-center and retrospective study, using a relatively small sample, limiting our conclusions. In XP patients' lesions, PRAME expression could help in the setting of challenging melanocytic tumors and surgical margins evaluation. It is also possible that the method can avoid overdiagnosis and, consequently, more aggressive treatment recommendation in unequivocal CM cases.

Double Immunohistochemical Labelling of PRAME and Melan A in Slow Mohs Biopsy Margin Assessment of Lentigo Maligna and Lentigo Maligna Melanoma

Introduction: Lentigo maligna (LM) and lentigo maligna melanoma (LMM) predominantly affect the head and neck areas in elderly patients, presenting as challenging ill-defined pigmented lesions with indistinct borders. Surgical margin determination for complete removal remains intricate due to these characteristics. Morphological examination of surgical margins is the key form of determining successful treatment in LM/LMM and underpin the greater margin control provided through the Slow Mohs micrographic surgery (SMMS) approach. Recent assessments have explored the use of immunohistochemistry (IHC) markers, such as Preferentially Expressed Antigen in Melanoma (PRAME), to aid in LM/LMM and margin evaluation, leveraging the selectivity of PRAME labelling in malignant melanocytic neoplasms. Methods: A Novel double-labelling (DL) method incorporating both PRAME and MelanA IHC was employed to further maximise the clinical applicability of PRAME in the assessment of LM/LMM in SMMS biopsies. The evaluation involved 51 samples, comparing the results of the novel DL with respective single-labelling (SL) IHC slides. Results: The findings demonstrated a significant agreement of 96.1% between the DL method and SL slides across the tested samples. The benchmark PRAME SL exhibited a sensitivity of 91.3% in the SMMS specimens and 67.9% in histologically confirmed positive margins. Discussion: This study highlights the utility of PRAME IHC and by extension PRAME DL as an adjunctive tool in the assessment of melanocytic tumours within staged excision margins in SMMS samples.

Updates on eyelid cancers

In this review, we aim to provide an overview of the five most common malignant eyelid tumors with current treatment recommendations based on international guidelines. Particular attention is paid to the clinicopathological correlation and the update with regard to adequate treatment. Newer systemic therapies enrich the existing treatment options, of which complete tumor excision remains the most important therapeutic measure.