PRAME immunohistochemistry as an adjunct for diagnosis and histological margin assessment in lentigo maligna

Melanocyte Density in the Diagnosis of Melanoma In Situ in Sun-Damaged Skin

ABSTRACT

Histologic differentiation between melanoma in situ in chronically sun-damaged skin (CSDS) [lentigo maligna (LM)] and CSDS without malignancy is difficult because signs of melanocyte activation and proliferation are found in both. A potentially reliable and quantifiable criterion is melanocyte density (MD). Here, we evaluated whether and to what extent MD allows the distinction between LM and CSDS, which is particularly relevant for the evaluation of borderline cases and surgical margins.Articles assessing MD in LM and/or CSDS were evaluated in a systematic review. The results were categorized and compared according to staining. Cutoff values were included whenever stated.Twenty articles matched the selection criteria. Six hundred forty-four samples of CSDS and 227 samples of LM were considered. In each individual study, mean MD scores were higher for LM than for CSDS. However, looking at the overall study situation, it becomes clear that the data are very heterogeneous and show overlaps. Therefore, no reliable orientation value can be derived. Only 1 article defined a cutoff value.The data of MD in LM in contrast to CSDS were sparse, and a defined cutoff value was only mentioned in 1 article for microphthalmia-associated transcription factor, which cannot yet be generalized. Especially regarding the importance for the definition of surgical resection margins, this unsatisfactory data set highlights the need for further studies. More precise diagnostic criteria could spare some patients extensive and possibly disfiguring surgery.

Analysis of PRAME immunocytochemistry in 109 acral malignant melanoma in situ

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

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.

Lentigo maligna: a review

Lentigo maligna (LM) is a melanoma in situ with distinct clinical features and histology. It commonly affects men after the sixth decade of life. Incidence rates of LM have increased based on early 21st century data from different countries; however, data are suboptimal. Data from England show a plateauing crude incidence between 2013 and 2019. By comparison, invasive melanoma and other types of melanoma in situ commonly appears in younger age groups (median age 58 and 67 years old, respectively) and incidence is rising. The most important risk factors for LM include fair skin and cumulative ultraviolet solar radiation exposure. Although LM is limited to the epidermis and connected skin adnexa, it may progress to invasive LM melanoma. The reported rate of malignant progression varies, reflecting a challenge for LM epidemiology research as often lesions are removed on diagnosis. LM poses a challenge in diagnosis and management. Although it can be diagnosed clinically or dermoscopically, histopathological assessment of biopsied skin tissue remains the gold standard. Reflectance confocal microscopy allows for better appreciation of the complexity of LM at a cellular level, often progressing beyond clinical margins. Management of LM may involve Mohs micrographic surgery or excision, although recurrence may occur even with 5 mm clinical margins. Imiquimod cream may be effective, but incomplete treatment and recurrence has been reported. Conservative management with observation or radiotherapy may be used in selected patients' cases. Five-year net survival rates are excellent. This paper reviews the natural history, epidemiology, aetiology, pathogenesis, diagnosis and management of LM.

An Update and Review of Clinical Outcomes Using Immunohistochemical Stains in Mohs Micrographic Surgery for Melanoma

BACKGROUND

Mohs micrographic surgery (MMS) provides optimal margin control through complete peripheral and deep margin assessment. The treatment of melanoma using MMS has historically been limited by difficulty in interpreting melanocytes using frozen sections. Immunohistochemical (IHC) staining, a technique whereby chromogen-tagged antibodies are used to detect antigens of interest, has revolutionized the surgical treatment of melanoma.

OBJECTIVES

This article provides an update and literature review of current IHC stains used in MMS for melanoma, their sensitivities and specificities, and clinical outcomes.

MATERIALS AND METHODS

A PubMed search was performed using keywords including "immunohistochemistry," "staining," and "Mohs surgery." Articles related to the use of IHC staining for the treatment of melanoma with MMS were included.

RESULTS

Six IHC stains met the criteria for the review including melanoma antigen recognized by T cells (MART-1), SRY-related HMG-box (SOX10), microphthalmia-associated transcription factor, HMB-45, MEL-5, S-100, and preferentially expressed antigen in melanoma.

CONCLUSION

The adaptation of IHC methods to frozen sections has enabled MMS to become a preferred treatment option for melanoma in special-site areas. Future studies are needed to standardize IHC techniques and to define best practices when using frozen section in the treatment of melanoma.

Shedding light on PRAME expression in dysplastic nevi: a cohort study

Dysplastic nevi represent one of the least agreed-upon entities in dermatopathology despite the existence of established criteria. This study explores preferentially expressed antigen in melanoma (PRAME) in dysplastic nevi, an uncharted area. We examined 22 common melanocytic nevi (CMN), 20 cutaneous melanomas (CM), 48 low-grade dysplastic nevi (LG-DN), and 40 high-grade dysplastic nevi (HG-DN). PRAME was immunohistochemically assessed using a five-tiered system (0 to 4 +). Among CMN, 59% scored 0, 32% scored 1 + , and 9% scored 2 + . CM had score 2 + and 4 + in 11% and 89% of cases, respectively. Among LG-DN, 38% presented score 0, 31% score 1 + , 17% score 2 + , 8% score 3 + , and 6% score 4 + . Thirty per cent of HG-DN demonstrated a score 0, 30% with score 1 + , 15% score 2 + , 10% score 3 + , and 15% score 4 + . Compared to CMN and CM, LG-DN and HG-DN showed heterogeneous expression profiles of PRAME. PRAME positivity effectively distinguished HG-DN from CM with 85% specificity and 80% sensitivity (p < 0.0001). Predictive values were 87% (negative) and 76% (positive). Furthermore, a trend of increased PRAME expression from LG-DN to HG-DN was observed. However, the applicability of PRAME in the differential diagnosis of dysplastic lesions remains unclear as can yield conflicting results with morphology, which remains the primary diagnostic tool for melanocytic lesions.

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.

Ancillary testing for melanoma: current trends and practical considerations

The diagnosis of melanocytic lesions is aided by ancillary testing, but clinical inspection with the histomorphological assessment on biopsy remains sufficient in most cases. Immunohistochemistry and molecular studies have proven useful for diminishing the pool of histomorphologically borderline lesions, and sequential testing may further improve overall diagnostic performance, but these assays should be used in a stepwise fashion if at all. Ancillary tests vary based on their technology, performance, and practical considerations, including but not limited to the specific diagnostic question, cost, and turn-around time, which impact test selection. This review examines currently used ancillary tests for the purpose of characterizing melanocytic lesions. Both scientific and practical considerations are discussed.

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

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

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.

Staged Excision of Lentigo Maligna of the Head and Neck: Assessing Surgical Excision Margins With Melan A, SOX10, and PRAME Immunohistochemistry

BACKGROUND

Staged excision has emerged as a superior treatment option for lentigo maligna (LM) of the head and neck when compared with conventional wide local excision. Assessing surgical excision margins for remaining LM poses a diagnostic challenge.

OBJECTIVES

To determine whether immunohistochemical (IHC) staining with SOX10 and preferentially expressed antigen in melanoma (PRAME) aids in diagnosing LM on excision margins compared with conventional hematoxylin and eosin and Melan A IHC staining.

METHODS

This study included cases of LM of the head and neck treated with staged excision. Histological findings were reviewed according to standard criteria for the diagnosis of LM and compared with the results after IHC staining for Melan A, SOX10, and PRAME.

RESULTS

The cohort consisted of 35 sections. Based on hematoxylin and eosin and Melan A IHC staining, 23 sections were diagnosed as LM by the initial pathologist. Further staining with SOX10 IHC showed only 8 to be consistent with a diagnosis of LM and 9 revealing features of actinic melanocyte hyperplasia. PRAME was positive in 5 of the 8 cases of LM and negative in all 9 cases of actinic melanocyte hyperplasia (P = 0.009). The presence of melanocyte nests (P = 0.29) and pagetoid spread (P = 0.003) was the most reliable histological findings distinguishing LM from its mimics.

CONCLUSION

SOX10 is a more specific and sensitive marker for melanocytes when assessing for LM on excision margins compared with Melan A. The addition of PRAME can be useful to confirm or exclude the diagnosis in challenging cases.

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.

Hyperplastic melanocytes with chromosomal aberrations in surrounding skin of subungual melanoma: fluorescence in situ hybridization analysis using whole-slide digital imaging

AIMS

Subungual melanoma (SUM) is increasingly being treated with conservative surgery. Consequently, the evaluation of resection margins has increased in importance. However, in several cases it is difficult to distinguish the in-situ lesion of SUM from hyperplastic melanocytes in surrounding skin. We examined whether PReferentially expressed Antigen in MElanoma (PRAME) immunohistochemistry and fluorescence in situ hybridization (FISH) labeling of CCND1 (11q13), RREB1 (6p25), MYB (6q23), and centromere 6 (CEP6) genes differentiated SUM from hyperplastic melanocytes.

METHODS AND RESULTS

We reviewed specimens of 36 SUM cases and compared PRAME immunostains of invasive melanoma, melanoma in situ, and hyperplastic melanocytes. PRAME-positive cases accounted for 90.5% of invasive melanoma, 88.9% of in situ melanoma, and 59.4% of hyperplastic melanocyte specimens. While invasive and in situ melanomas in more than half of examined cases were diffusely positive, this was found for only 9.4% of hyperplastic melanocyte cases. Four-colored FISH using whole-slide digital imaging was used to analyze positive detection rates and changes in chromosomal aberrations. The FISH positive detection rate was 100% in invasive melanomas, 94.7% in melanomas in situ, and 66.7% in hyperplastic melanocytes. The number of RREB1 (6p25) signals per cell was significantly amplified following tumor progression.

CONCLUSION

Hyperplastic melanocytes in the surrounding skin of SUM, considered morphologically non-neoplastic, showed chromosomal aberrations similar to those in melanoma. Such cells are also thought similar to the field cells of acral melanomas. Thus, whole-slide digital imaging is a technique that allows the evaluation of individual melanocyte lesions by FISH.

PRAME Expression Correlates With Genomic Aberration and Malignant Diagnosis of Spitzoid Melanocytic Neoplasms

ABSTRACT

Spitzoid melanocytic neoplasms are a diagnostically challenging class of lesions in dermatopathology. Recently, molecular assays and immunohistochemical markers have been explored as ancillary methods to assist in the diagnostic workup. Specifically, preferentially expressed antigen in melanoma (PRAME) immunohistochemistry is a nuclear stain commonly positive in melanomas, but not in nevi. This study investigates PRAME immunoreactivity (≥75% positive nuclear staining in tumor cells) in a set of 59 spitzoid melanocytic neoplasms with known clinical outcomes. We compared PRAME status with (1) the clinical outcomes, (2) the morphologic diagnoses, and (3) the status of TERT promoter mutation. Regarding clinical outcomes, 3 cases developed metastatic disease, of which 2 expressed diffusely positive PRAME staining. Of the 56 cases that did not show evidence of metastasis, 6 expressed diffusely positive PRAME staining. Morphologically, diffusely positive PRAME staining was seen in 7 of 21 cases (33.3%) diagnosed as melanoma and only 1 benign tumor 1 of 38 (2.6%). There were 4 of 8 cases with a TERT promoter mutation which were diffusely PRAME-positive compared with 4 of 51 cases without TERT promoter mutation ( P = 0.001). Our results show a statistically significant correlation between PRAME expression and the diagnosis, outcome, and TERT promoter mutation status of atypical spitzoid melanocytic neoplasms, suggesting immunohistochemistry for PRAME can help support a suspected diagnosis. However, because of occasional false-positive and negative test results, correlation with the clinical and histologic findings as well as results from other tests is needed for the interpretation of diagnostically challenging spitzoid melanocytic neoplasms.

Preferentially Expressed Nuclear Antigen in Melanoma Expression in Melanocytic Activation (Melanotic Macule) of the Nail Unit. A Potential Diagnostic Pitfall? A Study of 3 Cases

ABSTRACT

Recent studies have argued that melanocyte preferentially expressed nuclear antigen in melanoma (PRAME) is a sensitive and specific immunohistochemical marker of melanoma, including acral melanoma. In addition, loss of p16 expression has recently been suggested to have diagnostic utility in acral melanocytic tumors. The purpose of this study was to report PRAME expression in 3 cases of melanocytic activation (MAN). There were 2 men and 1 woman ranging in age at diagnosis from 46 years to 78 years (mean 61, 6 years). All cases involved a single digit. One lesion was in the fingernail (fifth finger), whereas the remaining 2 lesions were in the toenails (hallux). All the patient presented with a longitudinal melanonychia. The width of the lesions varied from 3 mm (2 cases) to 4 mm (1 case). The duration of the lesions before diagnosis varied from 12 to 24 months. Distinction of MAN from melanoma in situ is not always easy. Some morphological misleading features are illustrated in this study: (1) the suprabasal location of matrix melanocytes with long and thick dendrites within the 2-4 germinative cell layers; (2) the microconfluence of 2 melanocytes and rare melanocytes with a relatively large nucleus, however in a general context of melanocyte scarcity; and (3) the occasional nonspecific nuclear microphtalmia-associated transcription factor (MITF) staining of keratogeneous cells. Such staining could suggest a pagetoid spread of melanocytes in the keratogenous zone. PRAME antibody revealed a strong and diffuse staining in all cases. In addition, all cases were p16 negative. In this study, the melanocyte count inferior to 9 melanocytes/mm and the lack of nuclear atypia or confluence of melanocytes permitted a confident diagnosis of MAN. Limitations of our study lie largely in the small number of cases. Despite this, the expression of PRAME in some MAN seems to hamper its diagnostic value in differentiating benign from malignant lesion.

PRAME expression in melanocytic lesions of the nail

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Use of PRAME immunostaining to distinguish early melanoma in situ from benign pigmented conditions

BACKGROUND

PRAME (PReferentially expressed Antigen in MElanoma) is an antigen that shows marked overexpression in melanoma compared to normal skin melanocytes. PRAME immunohistochemistry has proven effective in distinguishing melanocytic nevi from melanoma, but it is unclear if it may be used to distinguish melanoma in situ from other benign pigmented lesions. In particular, differentiating from melanocytic hyperplasia in sun-damaged skin is sometimes clinically and histopathologically challenging. We hypothesized that PRAME staining of solar lentigo, sun-damaged skin, and melanoma in situ would aid in setting a threshold of positivity that could be useful in evaluating such conditions.

METHODS

We collected and stained typical examples of solar lentigo, melanoma in situ, and non-lesional sun-damaged skin by PRAME immunohistochemistry to assess a potential cutoff of PRAME positivity.

RESULTS

Solar lentigo and non-lesional sun-damaged skin had 10 or fewer PRAME-positive cells per millimeter (mean 1.2), on the other hand melanoma in situ had at least 16 (mean 75.1).

CONCLUSIONS

PRAME immunostaining appears sensitive and specific in the current series. This could be clinically useful for distinguishing melanoma in situ from benign melanocytic hyperplasia in sun-damaged skin. However, further studies are required to determine if 10 cells per millimeter is an acceptable threshold of positivity.

Cutaneous Melanomas: A Single Center Experience on the Usage of Immunohistochemistry Applied for the Diagnosis

Cutaneous melanoma (cM) is the deadliest of all primary skin cancers. Its prognosis is strongly influenced by the stage at diagnosis, with early stages having a good prognosis and being potentially treatable with surgery alone; advanced stages display a much worse prognosis, with a high rate of recurrence and metastasis. For this reason, the accurate and early diagnosis of cM is crucial-misdiagnosis may have extremely dangerous consequences for the patient and drastically reduce their chances of survival. Although the histological exam remains the "gold standard" for the diagnosis of cM, a continuously increasing number of immunohistochemical markers that could help in diagnosis, prognostic characterization, and appropriate therapeutical choices are identified every day, with some of them becoming part of routine practice. This review aims to discuss and summarize all the data related to the immunohistochemical analyses that are potentially useful for the diagnosis of cM, thus rendering it easier to appropriately applicate to routine practice. We will discuss these topics, as well as the role of these molecules in the biology of cM and potential impact on diagnosis and treatment, integrating the literature data with the experience of our surgical pathology department.

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

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

PRAME Immunohistochemistry of Spitzoid Neoplasms

BACKGROUND

Spitzoid melanocytic neoplasms are well known to be diagnostically challenging. Immunohistochemistry and molecular approaches have been used as ancillary diagnostic tests. Herein we investigate the use of PRAME immunohistochemistry (IHC) for the assessment of spitzoid melanocytic neoplasms.

METHODS

10 Spitz nevi, 14 atypical Spitz tumors, and 11 spitzoid melanomas were retrieved and PRAME IHC was scored on a scale of 1-4 (in % quartiles). Intensity of staining was categorized as weak or strong. Cases with no staining received a score of 0. Positive lymph nodes from three spitzoid melanomas were also analyzed.

RESULTS

Spitz nevi, atypical Spitz tumors, and spitzoid melanomas had mean PRAME IHC scores of 1.20, 0.93, and 3.36 respectively. The percentage of cases with a score 3 or higher for each category of spitzoid neoplasms are as follows: Spitz nevus (20%), atypical Spitz tumor (0%), and spitzoid melanoma (82%). Among the spitzoid melanomas, 3 cases had positive sentinel lymph nodes which demonstrated PRAME score of 2, 4, and 4 in the metastatic deposits.

CONCLUSIONS

Previous reports revealed PRAME IHC as useful to distinguish benign from malignant melanocytic lesions. The results presented here are concordant with the prior studies, but expand the application of this marker to Spitz nevi/tumors and spitzoid melanomas. The present findings suggest the potential diagnostic utility of PRAME IHC in the assessment of spitzoid melanocytic lesions, particularly in distinguishing spitzoid melanomas from Spitz nevi and atypical Spitz tumors. This article is protected by copyright. All rights reserved.

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.

Immunohistochemistry for Preferentially Expressed Antigen in Melanoma in the Differential Diagnosis of Melanocytic Lesions of the Nail Apparatus

ABSTRACT

Nail unit melanocytic lesions present a unique set of diagnostic challenges because of the unfamiliarity with clinical assessment and the lack of experience with histologic examination. Because the first surgical specimen received in the pathology laboratory is typically small, sometimes suboptimal biopsy, the distinction between melanoma and its histologic mimics can be difficult. For this reason, there has been a continued interest in the development of ancillary markers that may assist in the differential diagnosis of nail unit melanocytic lesions. Upregulation of preferentially expressed antigen in melanoma (PRAME) has been reported to be a common event in melanomas, and PRAME immunohistochemistry has been shown to be helpful in evaluating various melanocytic neoplasms. In this study, we evaluated PRAME protein expression in a series of nail unit melanocytic lesions. Twenty-five nail unit melanomas (including small biopsy and amputation specimens) and 32 control benign melanocytic lesions were retrospectively retrieved. Nuclear PRAME staining was scored as percentage and intensity labeling. All melanoma cases showed the nuclear expression of PRAME, which was usually diffuse and strong. In specimens where the neoplastic cells are limited in number, the staining was restricted to the tumor cells, corresponding to the initial H&E impression. All control cases were negative for PRAME expression. PRAME expression is helpful in distinguishing between melanomas and other nail unit melanocytic lesions. This antibody also proved to be diagnostically valuable in detecting melanoma cells in small specimens with minimal disease.

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.

PRAME expression in cellular neurothekeoma: A study of 11 cases

BACKGROUND

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

MATERIALS

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

RESULTS

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

CONCLUSIONS

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

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

Simple Summary

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

Abstract

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

PRAME expression in melanocytic lesions of the conjunctiva

AIMS

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

METHODS AND RESULTS

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

CONCLUSION

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

Melanocytic hyperplasia associated with surgical scars in basal cell carcinoma re-excision specimens: A single-center retrospective study

BACKGROUND

Melanocytic hyperplasia (MH) overlying surgical scars has been reported but MH adjacent to the scar has not been previously addressed.

METHODS

We evaluated scar-associated MH in 489 re-excision specimens of basal cell carcinoma. Melanocytic density, confluence, atypia, suprabasal scatter, follicular extension, distance from the scar, correlation with clinicopathologic parameters, and PRAME expression were recorded.

RESULTS

One hundred seventy-seven of 489 (36%) cases exhibited MH beyond the scar extending to 6.65 mm median distance, with a median density of 13 melanocytes/0.5 mm (6-24 mm), confluence in 74 (42%) cases, atypia in 14 (8%), suprabasal melanocytes in 25 (14%), and follicular extension in 21 (12%). Mean age of MH group was significantly lower than non-MH group (P < 0.0001). MH overlying the scar was significantly higher in specimens with elastosis than those without elastosis (P < 0.0001). PRAME expression was absent in 14 of 20 cases and present in rare melanocytes in 6 cases.

CONCLUSIONS

Increased melanocytic density with confluence, mild atypia, suprabasal scatter, and superficial follicular extension may be observed in re-excision specimens adjacent to surgical scars in the absence of a melanocytic neoplasm. These observations are helpful for appropriate interpretation of melanoma re-excision specimens, to avoid potential pitfalls in diagnosis and unnecessary therapeutic measures.

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

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