MITF accurately highlights epidermal melanocytes in atypical intraepidermal melanocytic proliferations

Utilizing deep learning model for assessing melanocytic density in resection margins of lentigo maligna

BACKGROUND

Surgical excision with clear histopathological margins is the preferred treatment to prevent progression of lentigo maligna (LM) to invasive melanoma. However, the assessment of resection margins on sun-damaged skin is challenging. We developed a deep learning model for detection of melanocytes in resection margins of LM.

METHODS

In total, 353 whole slide images (WSIs) were included. 295 WSIs were used for training and 58 for validation and testing. The algorithm was trained with 3,973 manual pixel-wise annotations. The AI analyses were compared to those of three blinded dermatopathologists and two pathology residents, who performed their evaluations without AI and AI-assisted. Immunohistochemistry (SOX10) served as the reference standard. We used a dichotomized cutoff for low and high risk of recurrence (≤ 25 melanocytes in an area of 0.5 mm for low risk and > 25 for high risk).

RESULTS

The AI model achieved an area under the receiver operating characteristic curve (AUC) of 0.84 in discriminating margins with low and high recurrence risk. In comparison, the AUC for dermatopathologists ranged from 0.72 to 0.90 and for the residents in pathology, 0.68 to 0.80. Additionally, with aid of the AI model the performance of two pathologists significantly improved.

CONCLUSIONS

The deep learning showed notable accuracy in detecting resection margins of LM with a high versus low risk of recurrence. Furthermore, the use of AI improved the performance of 2/5 pathologists. This automated tool could aid pathologists in the assessment or pre-screening of LM margins.

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.

Pitfalls in Cutaneous Melanoma Diagnosis and the Need for New Reliable Markers

Cutaneous melanoma is one of the most aggressive forms of skin cancer, with the development of advanced stage disease resulting in a high rate of patient mortality. Accurate diagnosis of melanoma at an early stage is essential to improve patient outcomes, as this enables treatment before the cancer has metastasised. Histopathologic analysis is the current gold standard for melanoma diagnosis, but this can be subjective due to discordance in interpreting the morphological heterogeneity in melanoma and other skin lesions. Immunohistochemistry (IHC) is sometimes employed as an adjunct to conventional histology, but it remains occasionally difficult to distinguish some benign melanocytic lesions and melanoma. Importantly, the complex morphology and lack of specific biomarkers that identify key elements of melanoma pathogenesis can make an accurate confirmation of diagnosis challenging. We review the diagnostic constraints of melanoma heterogeneity and discuss issues with interpreting routine histology and problems with current melanoma markers. Innovative approaches are required to find effective biomarkers to enhance patient management.

Genodermatoses associated with melanocytic nevi

Though melanocytic nevi are ubiquitous in the general population, they can also be key cutaneous manifestations of genetic syndromes. We describe genodermatoses associated with melanocytic nevi and discuss their clinical characteristics, cutaneous manifestations, underlying genetics, and, if applicable, guidelines for when genetic testing should be performed. We categorized these genodermatoses based on their association with congenital nevi, acquired nevi, or nevi whose first appearance is unknown. In many cases, the distinctive morphology or distribution of melanocytic nevi can be an important clue that an underlying genetic syndrome is present, allowing both the patient as well as family members to be screened for the more serious complications of their genetic disorder and receive education on potential preventative measures. As we continue to advance our understanding of how various genotypes give rise to the wide spectrum of phenotypes observed in these genodermatoses, we shall be able to better stratify risk and tailor our screening methods to clinically manage the heterogeneous manifestations of genodermatoses among these patients.

Lichenoid dermatoses with pseudomelanocytic nests vs inflamed melanoma in situ: A comparative study

AIMS

Pseudomelanocytic nests or "pseudonests" arising in lichenoid dermatoses can be a diagnostic pitfall for melanoma in situ (MIS), especially on sun-damaged skin. We sought to evaluate histopathological features that may be helpful in distinguishing this benign process from inflamed MIS.

METHODS

Ten biopsy specimens containing pseudomelanocytic nests within lichenoid dermatoses and twenty cases of inflamed MIS were retrospectively reviewed. Cases with pseudomelanocytic nests represented either a rash (n = 6) or a discrete non-melanocytic lesion, such as lichenoid keratosis (n = 4).

RESULTS

All cases with pseudomelanocytic nests showed nests of microphthalmia-associated transcription factor-positive cells at the dermoepidermal junction (DEJ) with interface changes and lichenoid inflammation. Pagetoid scatter, confluence of solitary melanocytes at the DEJ and significant cytologic atypia was not seen in any of these cases. In contrast, all cases of inflamed MIS demonstrated confluence of single melanocytes at the DEJ with cytologic atypia (P < 0.001) and 18/20 cases showed pagetoid scatter of melanocytes (P = 0.001).

CONCLUSIONS

Our results show that, of the different histopathological features assessed, confluent growth and pagetoid scatter of atypical melanocytes were seen in most cases of inflamed MIS but were absent in all cases with pseudomelanocytic nests. Therefore, in addition to clinicopathological correlation, these features may be useful in differentiating pseudomelanocytic nests arising in lichenoid dermatoses from inflamed MIS.

Digital Quantification of Melanocytic Density in Resection Margins of Lentigo Maligna Using SOX10 Versus Hematoxylin-Eosin Staining

ABSTRACT

Lentigo maligna (LM) represents an overgrowth of atypical melanocytes at the dermal-epidermal junction of chronically sun-damaged skin. The presence of LM on sun-damaged skin poses a diagnostic challenge because the solar-induced melanocytic hyperplasia makes it difficult to assess the LM margins. Melanocytic density can be used to discriminate sun-damaged skin from LM. The aim of this study was to quantify the melanocytic density at the surgical margins of scanned whole-slide images of LM comparing sections stained with H&E and SOX10. Twenty-six surgically excised LM diagnosed at the Department of Pathology at Sahlgrenska University Hospital were collected. The slides that contained the closest surgical margin or harbored the highest density of melanocytes at the margin were selected for serial sectioning using H&E and SOX10. Whole-slide imaging at ×40 magnification was used, and a circular field with a diameter of 0.5 mm at the surgical margin was superimposed on the image. Five blinded pathologists reviewed the slides in a randomized order. In the majority of the cases (24/26), the pathologists identified more melanocytes on the SOX10 slides than those on the H&E slides. On average, 2.5 times more melanocytes were counted using SOX10 compared with H&E (P < 0.05). Furthermore, the average group SD on the H&E slides was 4.12 compared with 2.83 on the SOX10 slides (P = 0.004). Thus, the use of SOX10 staining leads to higher melanocytic density counts compared with H&E staining when assessing the surgical margins of LM. The use of SOX10 staining also significantly decreased the interobserver variability between pathologists.

Defining the Histopathological Term Atypical Intraepidermal Melanocytic Proliferation: A Retrospective Cross-Sectional Study

BACKGROUND

Atypical intraepidermal melanocytic proliferation (AIMP) is a general term assigned to melanocytic proliferations of uncertain biological potential when a definitive histopathological diagnosis cannot be achieved. There are few data available describing the possibility of malignancy of AIMP, or ways to further define diagnosis.

OBJECTIVE

To determine the rate of diagnostic change of AIMP to melanoma or melanoma in situ (MIS) after conventional excision. In addition, to determine the role of immunohistochemistry (IHC) in defining AIMP biopsies.

METHODS

Retrospective cross-sectional, single-center review of biopsies with a diagnosis of AIMP with a follow-up conventional excision from 2012-2016 was performed. In a separate analysis, a search was performed for AIMP biopsied lesions in which IHC was subsequently performed.

RESULTS

The rate of diagnostic change of AIMP to MIS was 4.8% (8/167) after excision. Punch biopsy was a risk factor for diagnostic change to MIS (odds ratio 12.94, confidence interval 2.56-65.38, P = 0.008). The rate of diagnostic change of AIMP biopsies after examining with IHC was 21.3% (34/160) to MIS and 4.4% (7/160) to melanoma.

CONCLUSION

The possibility of malignancy of AIMP lesions must be taken into consideration when counseling patients and when planning treatment options. IHC is a useful tool and should be used in the evaluation of AIMP specimens.

Is melanocyte density our last hope? Comparison of histologic features of photodamaged skin and melanoma in situ after staged surgical excision with concurrent scouting biopsies

Differentiating melanocytic hyperplasia (MH) on photodamaged skin from junctional lentiginous melanocytic proliferations (JLMP), early evolving melanoma in situ (MIS), or the periphery of a lesion of MIS on staged excision can be challenging. Although previous cross-sectional studies have elucidated important criteria for distinguishing MH on photodamaged skin from more concerning lesions, this study highlights a technique to treat JLMP and MIS with staged mapped excision and baseline scouting biopsies of adjacent nonlesional photodamaged skin to assist in determination of surgical margin clearance. Additionally, we compare the lesional and photodamaged control biopsies from the same patient to evaluate relevant histologic criteria that may be used to distinguish MH in photodamaged skin from JLMP/MIS, while minimizing confounding factors. There was a statistically significant difference (P ≤ 0.05) found for melanocyte density, irregular melanocyte distribution, melanocyte clustering, follicular infundibulum involvement, and nesting. However, criteria such as nesting, epithelioid cells and melanocyte clustering were seen in both photodamaged skin and MIS. These findings underscore the fact that histologic features of photodamaged skin can overlap with the histopathological features of MIS. Of all of the criteria evaluated, melanocytic density was the most objective histologic criterion and did not show overlap between the sun-damaged and JLMP/MIS groups.

Immunohistochemistry in Dermatopathology and its Relevance in Clinical Practice

Immunohistochemistry (IHC) is an important diagnostic tool in histopathology. Dermatopathology is a rapidly developing subspecialty of histopathology. Although IHC is not widely used in routine dermatopathology practice, its application is gradually increasing. IHC is used to differentiate two conditions with similar morphology, to confirm a diagnosis as well as to assess prognosis. It is more commonly used for neoplastic conditions like melanocytic, hematolymphoid, and spindle cell tumors, although uses can be very wide. Although IHC can aid in diagnosis, sometimes interpretation can be difficult as there may be overlapping findings. Thus, IHC should not be interpreted in isolation and should be done in the context of clinical and histological findings. In this review, we have discussed the uses of various immunohistochemical markers in dermatopathology in the light of current literature and their clinical relevance.

MART-1-labeled melanocyte density and distribution in actinic keratosis and squamous cell cancer in situ: Pagetoid melanocytes are a potential source of misdiagnosis as melanoma in situ

BACKGROUND

Actinic keratosis (AK) and squamous cell carcinoma in-situ (SCCIS) within or near melanoma in situ (MIS) can complicate diagnosis due to overlapping clinical and microscopic features. This study aimed to describe basilar melanocyte density and pagetoid spread in AK and SCCIS for improved diagnostic accuracy.

METHODS

A total of 22 AK and 22 SCCIS biopsies containing a margin of uninvolved epidermis were immunostained with MART-1 (melanoma antigen recognized by T-cells 1). The basilar melanocyte:keratinocyte ratio and the number and distribution of pagetoid melanocytes were compared in AK, SCCIS, and uninvolved epidermis. An in-vitro human skin model was created to assess the impact of keratinocyte atypia on melanocyte distribution.

RESULTS

The median basilar melanocyte:keratinocyte ratio in SCCIS (1:11.49) was lower than in uninvolved epidermis (1:5.59, P = 0.0011), and the ratio in AK (1:6.94) was similar to uninvolved epidermis (P = 0.987). Pagetoid melanocytes were absent in perilesional skin but common in AK (21/22, P < 0.0001) and SCCIS (22/22, P < 0.0001). Pagetoid melanocytes at or above the mid-spinous layer were more common in SCCIS (21/22) vs AK (7/22, P < 0.0001). Pagetoid melanocytes were present in the in-vitro skin model made with neoplastic but not normal keratinocytes.

CONCLUSIONS

Pagetoid melanocytes in AK and SCCIS should be interpreted with caution to avoid overdiagnosis of MIS.

Ultraviolet radiation induces Melan-A-expressing cells in interfollicular epidermis in wild-type mice

Adult wild-type mice are not supposed to be proper models for ultraviolet radiation (UVR)-induced melanoma since melanocytes are confined to hair follicles and cannot be sufficiently reached by UVR. On the other hand, in mutated mouse models used for melanoma research limitations, including an altered immune system and selection of affected pathways, lead to tumors phenotypically quite different from naturally occurring melanomas. We compared the distribution of epidermal melanocytes in UVR and not-UVR-exposed wild-type C57BL/6 mice. Starting at the age of 8 weeks, mice were exposed to physiologic doses of UVR three times weekly over 16 weeks. Back skin biopsies were taken 4, 8, 12 and 16 weeks after initiation of exposure, and stained for Melan-A, representing a highly selective marker for melanocytes. Surprisingly, after exposure to UVR, Melan-A positive cells were detected also in the interfollicular epidermis of C57BL/6 mice. We conclude that UVR is capable of inducing interfollicular epidermal melanocytes in wild-type mice.

Atypical Melanocytic Proliferations: A Review of the Literature

BACKGROUND

Ambiguous histopathologic diagnoses represent a challenge for clinicians because of a lack of definitive diagnosis and related uncertainty about management.

OBJECTIVE

To review the literature on atypical melanocytic proliferations and detail synonymous terms, epidemiology, diagnostic work-up, histopathology, treatment, and prognosis.

METHODS

Databases from PubMed and Web of Science were searched for articles related to atypical melanocytic proliferations.

RESULTS

Intraepidermal melanocytic proliferations with features worrisome for possible melanoma in situ (MIS) are generally excised as for MIS. Reported rates of upstaging of such cases to invasive melanoma on review of the excision are very low. Because invasion, lymph node spread, and metastasis can occur in atypical melanocytic lesions with a thick intradermal component, these are often treated as for malignant melanoma.

CONCLUSION

Because the diagnosis dictates treatment, it is incumbent to establish a diagnosis as definitive as possible, obtaining second or third opinions and using ancillary studies when appropriate. When the diagnosis remains uncertain, it is difficult to provide guidelines for treatment. Clinical care decisions for patients with an uncertain diagnosis are best done on a case-by-case basis weighing probabilities of adverse outcomes against potential benefits and risks from various treatment options.

Histopathologic and Immunohistochemical Correlates of Confocal Descriptors in Pigmented Facial Macules on Photodamaged Skin

Importance

Pigmented facial macules on photodamaged skin are a clinical, dermoscopic, and histopathologic challenge.

Objectives

To clinically and dermoscopically characterize, by means of reflectance confocal microscopy (RCM), ambiguous pigmented facial macules and establish a correlation between RCM, histopathologic, and immunohistochemical findings.

Design, Setting, and Participants

A prospective study of ambiguous pigmented facial macules on photodamaged skin was conducted in a tertiary referral center for dermatology between January 1, 2009, and December 31, 2015. Sixty-one patients with 63 ambiguous pigmented facial macules and 12 control photodamaged facial areas were included in the study. Melanocyte density in 1-mm basal layers was determined in skin biopsy specimens from all lesions stained with hematoxylin-eosin and immunohistochemical markers (melan-A, microphthalmia-associated transcription factor, and SRY-related HMG-box gene 10). Dermoscopic, RCM images, and histopathologic preparations were systematically evaluated for the presence of lentigo maligna (LM) criteria. Confocal evaluation was blinded to clinical and dermoscopic diagnosis. Sensitivity and specificity of RCM for LM diagnosis and κ value to establish correlations between dermoscopy, RCM, and histopathology were performed.

Main Outcomes and Measures

Sensitivity and specificity of RCM for LM diagnosis.

Results

Of the 61 patients included in the study, 31 (51%) were women; mean (SD) age was 71.8 (13.1) years. Twenty-four of the 63 (38%) lesions were diagnosed as LM or LM melanoma (LMM) and 39 (62%) as benign pigmented lesions. Reflectance confocal microscopy enhanced the diagnosis of pigmented facial macules with 91.7% sensitivity and 86.8% specificity. Multivariate analysis showed 2 dermoscopic and 2 confocal features associated with LM or LMM: (1) asymmetric follicular pigmentation and targetlike structures, and (2) round, large pagetoid cells and follicular localization of atypical cells, respectively. Continuous proliferation of atypical melanocytes was found in 21 (88%) LM or LMM and in 3 (77%) benign lesions. Asymmetric pigmented follicular openings by dermoscopy correlated with follicular localization of pagetoid cells by RCM (κ = 0.499, P < .001). The presence of 3 or more atypical cells at the dermal-epidermal junction (DEJ) by RCM correlated with hyperplasia of melanocytes in hematoxylin-eosin sections (κ = 0.422, P < .001).

Conclusions and Relevance

Reflectance confocal microscopy improves LM diagnosis in photodamaged skin with good histopathologic correlation although false-positive and false-negative cases exist. False-positives obtained with RCM in photodamaged skin are due to the presence of basal melanocyte hyperplasia and intraepidermal Langerhans cells. Histopathologic features of these lesions sometimes are not enough for a definite diagnosis and immunohistochemical studies may be required.

Frequency of and factors associated with positive or equivocal margins in conventional excision of atypical intraepidermal melanocytic proliferations (AIMP): A single academic institution cross-sectional study

BACKGROUND

No evidence-based surgical guidelines exist for atypical intraepidermal melanocytic proliferation (AIMP), a descriptive histopathologic diagnosis with uncertain malignant potential.

OBJECTIVE

We sought to identify the frequency of and risk factors associated with positive or equivocal margins after conventional excision.

METHODS

We conducted a retrospective cross-sectional study of 413 AIMPs treated by conventional excision.

RESULTS

Positive or equivocal margins were seen in 2.9% (12/413) of conventional excisions of AIMP. Risk factors associated with positive or equivocal margins included anatomic location on the head and neck (5/51, 9.8%; odds ratio 6.91, 95% confidence interval 1.93-24.80) (P = .012) and a preoperative biopsy specimen that included melanoma in situ in the differential diagnosis (11/214, 5.1%; odds ratio 10.73, 95% confidence interval 1.37-83.88) (P = .006). The frequency of positive or equivocal margins did not differ significantly with surgical margins greater than or less than 5 mm (odds ratio 0.61, 95% confidence interval 0.18-2.07) (P = .457).

LIMITATIONS

This was a single-site, retrospective observational study.

CONCLUSION

AIMP has a significantly increased risk for incomplete excision when it is located on the head and neck or has a preoperative histologic differential diagnosis that includes melanoma in situ. These subsets of AIMP may benefit from Mohs micrographic surgery or staged surgical excision to confirm clear margins before reconstruction.

Lentigo maligna - anatomic location as a potential risk factor for recurrences after non-surgical treatment

Background

A higher incidence of lentigo maligna (LM) recurrences on the nose was previously observed in our cohort after non‐surgical treatment.

Objectives

To determine histological parameters that might be related to the previously observed higher incidence of LM recurrences on the nose after non‐surgical treatment.

Methods

We randomly selected 22 surgical specimens of LM on the nose and 22 on the cheek. Histopathological analysis was performed on haematoxylin and eosin stained and microphthalmia transcription factor immunohistochemically stained slides. The number of pilosebaceous units (PSU) per mm, maximum depth of atypical melanocytes along the skin appendages and maximum depth of the PSU itself were determined.

Results

The nose had a significantly higher density of PSU than the cheek. The atypical melanocytes extended deeper along the PSU on the nose with a mean (SD) depth of 1.29 mm (0.48) vs. a mean depth of 0.72 mm (0.30) on the cheek (P < 0.001). The maximum depth of the PSU on the nose was greater than on the cheek, mean (SD) depth of 2.28 mm (0.41) vs. 1.65 mm (0.82) (P = 0.003).

Conclusions

The higher recurrence risk of LM on the nose after non‐surgical treatment that we previously observed in our cohort is most likely based on a higher density of atypical melanocytes and also their deeper extension into the follicles. These results shed more light on our previous findings and learn that anatomical location is relevant for the risk of recurrence of LM after non‐surgical treatment.

Expression of microphthalmia transcription factor, S100 protein, and HMB-45 in malignant melanoma and pigmented nevi

Malignant melanoma (MM) is a type of malignant tumor, which originates from neural crest melanocytes. MM progresses rapidly and results in a high mortality rate. The present study aims to investigate the expression of microphthalmia transcription factor (MITF), the S100 protein, and HMB-45 in MM and pigmented nevi. A total of 32 MM samples (including three skin metastasis, three lymph node metastasis and two spindle cell MM samples), two Spitz nevus samples, four pigmented nevus samples and two blue nevus samples were collected. The expression levels of S100 protein, HMB-45, and MITF were observed via immunostaining. The S100 protein exhibited high positive rates in MM and pigment disorders (96.7 and 100%, respectively), but with low specificity. The S100 protein was also expressed in fibroblasts, myoepithelial cells, histocytes and Langerhans cells in normal skin samples. HMB-45 had high specificity. Its positive expression was only confined to MM cells and junctional nevus cells. Furthermore, HMB-45 was not expressed in melanocytes in the normal tissue samples around the tumor or in the benign intradermal nevus cells. MITF exhibited high specificity and high sensitivity. It was expressed in the nuclei of melanocytes, MM cells and nevus cells. It was observed to be strongly expressed in metastatic MM and spindle cell MMs. Thus, MITF may present as a specific immunomarker for the diagnosis and differential diagnosis of MM.

Immunohistochemistry in dermatopathology

CONTEXT

Immunohistochemistry is not a diagnostic test but a highly valuable tool that requires interpretation within a context.

OBJECTIVE

To review the current status and limitations of immunohistochemistry in dermatopathology.

DATA SOURCES

English-language literature published between 1980 and 2014.

CONCLUSIONS

Although immunohistochemistry is rarely completely specific or sensitive, it is an important adjunctive technique in dermatopathology and can be helpful in a series of diagnostic dilemmas.

Diagnostic Immunohistochemistry in Cutaneous Neoplasia: An Update

Immunohistochemistry (IHC) is an important adjunct in the diagnosis of neoplastic skin diseases. In addition to the many established IHC markers currently in use, new markers continue to emerge, although their general acceptance and routine application requires robust validation. Here, we summarize the most well-established and commonly used biomarkers along with an array of newer ones reported in the past several decades that either demonstrate or hold high clinical promise in the field of cutaneous pathology. We also highlight recent applications of novel IHC markers in melanoma diagnosis including genetic mutation status markers [e.g. BRAF (v-raf murine sarcoma viral oncogene homolog B) and NRAS (neuroblastoma RAS viral oncogene homolog)] and an epigenetic alteration marker (e.g. 5-hydroxymethylcytosine). We specifically focus on the role of IHC in the differential diagnosis of cutaneous lesions that fall under the following categories: melanoma, epidermal tumors with an intraepidermal epitheliomatous pattern, spindle cell lesions of the dermis, small round blue cell tumors of the dermis, and cutaneous adnexal tumors. While IHC is a valuable tool in diagnostic dermatopathology, marker selection and interpretation must be highly informed by clinical context and the histologic differential diagnosis. With rapid progress in our understanding of the genetic and epigenetic mechanisms of tumorigenesis, new IHC markers will continue to emerge in the field of diagnostic dermatopathology.

Emerging clinical applications of selected biomarkers in melanoma

Melanoma is a lethal skin disease with a mostly predictable clinical course according to a known constellation of clinical and pathologic features. The distinction of melanoma from benign melanocytic nevus is typically unequivocol; however, there is a subset of tumors known for its diagnostic challenges, development of late metastases, and difficulties in treatment. Several melanocytic tissue biomarkers are available that can facilitate the histopathologic interpretation of melanoma as well as provide insight into the biologic potential and mutational status of this disease. This review describes the clinical application of some of these established and emerging tissue biomarkers available to assess melanocytic differentiation, vascular invasion, mitotic capacity, and mutation status. The selected tissue biomarkers in this review include MiTF, Sox10, D2-40, PHH3, H3KT (anti-H3K79me3T80ph), anti-BRAFV600E, and anti-BAP-1.