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

Restrospective reappraisal of the prognostic classification of spitzoid melanocytic neoplasms after BRAF and NRAS mutation characterisation: a single institution experience

AIMS

The current WHO classification of melanocytic tumours excludes neoplasms showing BRAF or NRAS mutations from the Spitz category. This study aimed to review and reclassify atypical melanocytic tumours with spitzoid morphological features diagnosed between 2009 and 2021 in our hospital after expanding the molecular profile, including BRAF and NRAS mutations in all cases.

METHODS AND RESULTS

A total of 71 neoplasms showing spitzoid features (Spitz-like) and atypia were included. The risk of progression of tumours was first studied by integrating the morphology, immunohistochemistry (p16, Ki67, HMB45 and PRAME) and fluorescence in-situ hybridisation (FISH) results (melanoma multiprobe and 9p21). In a second step, after expanding the molecular study, including BRAF and NRAS mutational status, the neoplasms were finally classified into four subgroups: atypical Spitz tumour (AST, n = 45); BRAF-mutated naevus/low-grade melanocytoma with spitzoid morphology (BAMS, n = 2); Spitz melanoma (SM, n = 14); and BRAF or NRAS mutated melanoma with spitzoid features (MSF, n = 10). Follow-up of patients revealed uneventful results for AST and BAMS. Only one SM presented lymph node metastasis after 134 months. Conversely, patients with MSF showed an unfavourable outcome: three developed lymph node metastases after a mean time of 22 months, with one patient presenting distant metastasis and dying of the disease 64 months from diagnosis. The progression-free survival showed significant differences between the four groups of spitzoid tumours (P < 0.001) and between both melanoma subtypes (P = 0.012).

CONCLUSIONS

The classification and prognostication of atypical neoplasms with spitzoid features requires the integration of histomorphology with the molecular investigation of tumours, which should include BRAF and NRAS mutational status.

Spitz Melanocytic Tumors: A Fascinating 75-Year Journey

Over the last 75 years, our understanding of Spitz lesions has undergone substantial evolution. Initially considered a specific type of melanoma, the perception has shifted towards recognizing Spitz lesions as a spectrum comprising Spitz nevi, Spitz melanocytomas, and Spitz melanomas. Spitz lesions are known for posing a significant diagnostic challenge regarding the distinction between benign neoplasms displaying atypical traits and melanomas. A comprehensive understanding of their molecular basis and genomic aberrations has significantly improved precision in classifying and diagnosing these challenging lesions. The primary aim of this review is to encapsulate the current understanding of the molecular pathogenesis and distinct clinicopathologic characteristics defining this intriguing set of tumors.

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.

PRAME Is an Effective Tool for the Diagnosis of Nevus-Associated Cutaneous Melanoma

(1) Background: Nevus-associated cutaneous melanoma (CM) is relatively common in the clinical practice of dermatopathologists. The correct diagnosis and staging of nevus-associated cutaneous melanoma (CM) mainly relies on the correct discrimination between benign and malignant cells. Recently, PRAME has emerged as a promising immunohistochemical marker of malignant melanocytes. (2) Methods: PRAME immunohistochemistry (IHC) was performed in 69 cases of nevus-associated CMs. Its expression was evaluated using a score ranging from 0 to 4+ based on the percentage of melanocytic cells with a nuclear expression. PRAME IHC sensitivity, specificity, positive predictive values, and negative predictive values were assessed. Furthermore, the agreement between morphological data and PRAME expression was evaluated for the diagnosis of melanoma components and nevus components. (3) Results: PRAME IHC showed a sensitivity of 59%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 71%. The diagnostic agreement between morphology and PRAME IHC was fair (Cohen's Kappa: 0.3); the diagnostic agreement regarding the benign nevus components associated with CM was perfect (Cohen's Kappa: 1.0). PRAME was significantly more expressed in thick invasive CMs than in thin cases (p = 0.02). (4) Conclusions: PRAME IHC should be considered for the diagnostic evaluation of nevus-associated CM and is most useful in cases of thick melanomas. Pathologists should carefully consider that a PRAME-positive cellular population within the context of a nevus could indicate a CM associated with the nevus. A negative result does not rule out this possibility.

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.

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.

Modern Concepts in Melanocytic Tumors

The advent of molecular pathology has fueled unprecedented advances in the diagnosis and understanding of melanocytic tumors. These advances, however, have also generated concepts that may be difficult to grasp for clinical practitioners, who are not always conversant with the array of genetic techniques employed in the laboratory. These same practitioners, however, are being increasingly called on to provide treatments that are often based on the latest molecular findings for melanocytic tumors. We review the most recent concepts in the pathway classification of melanocytic tumors, including intermediate lesions known as melanocytomas. We examine the genetic and molecular techniques used to study these tumors, look at where they overlap, and discuss their limitations and some of the most difficult-to-interpret results.