Immunostaining for MART-1 in the interpretation of problematic intra-epidermal pigmented lesions

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.

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.

Lentigo maligna: review of salient characteristics and management

Lentigo maligna is a melanocytic neoplasm, often regarded as 'melanoma in situ,' which may progress to lentigo maligna melanoma. Lentigo maligna clinically presents as a pigmented, asymmetric macule that originates on the head and neck and spreads slowly. The preferred method for diagnosing lentigo maligna is excisional biopsy. Histology shows proliferation of atypical melanocytes at the epidermal-dermal junction in small nests or single cells. The differential diagnosis includes solar lentigo, seborrheic keratosis, lichen planus-like keratosis, pigmented actinic keratosis, and melanocytic nevus. Stains used in diagnosis include hematoxylin and eosin, HMB-45, MART-1/Melan-A, Mel-5, and S-100. Surgical excision is the preferred treatment for lentigo maligna. Second-line techniques include medical (topical imiquimod) and destructive therapy.

Differences in tumor thickness between hematoxylin and eosin and Melan-A immunohistochemically stained primary cutaneous melanomas

Tumor thickness (Breslow thickness) represents the main prognostic factor in primary melanoma. Potential differences in melanoma tumor thickness measurements between conventional hematoxylin and eosin (H&E) and Melan-A immunohistochemical staining were evaluated. Ninety-nine excisional biopsies were included in the study. From each sample, 2 consecutive histological sections were stained with H&E and Melan-A, respectively. Tumor thickness was measured from both sections by 2 independent observers. In 59 biopsy specimens (59.6%), higher tumor thickness measurements were recorded in Melan-A-stained than in H&E-stained sections. In 42.4% of such cases (25 biopsies), the observed differences were ≥0.2 mm. After Melan-A evaluation, 33% of in situ melanoma cases were reclassified as invasive melanoma, with thickness measurements ranging from 0.15 to 0.35 mm. In 23 biopsies, identical values were recorded with both techniques, whereas in 17 cases, measurements obtained with H&E staining were slightly higher (from 0.01 to 0.18 mm) than those obtained with Melan-A staining. A high rate of interobserver agreement was noted, and significant intertechnique measurement differences were detected. Significant discrepancies (≥0.2 mm) in thickness measurements between the 2 techniques were mainly attributed to the presence of individual or small clusters of melanocytic cells in the papillary dermis. These melanocytic cells could be easily overlooked in H&E-stained sections, especially in sections showing dense lymphohistiocytic inflammatory infiltrates, numerous melanin-containing histiocytic cells in the upper dermis, or extensive fibrotic changes or regression phenomena. This study confirms the practical interest of immunohistochemical staining with Melan-A in evaluating primary melanoma and, specifically, in situ melanoma cases.

Update on immunohistochemistry in melanocytic lesions

This article is an up-to-date overview of the potential uses and limitations of immunohistochemistry (IHC) in melanocytic lesions. The information is intended to assist dermatopathologists and dermatologists who read slides to appropriately use IHC in this setting. In addition, dermatologists who do not review microscopic slides will better understand the rationale of the pathologist when reading and interpreting the pathology report.

Immunohistochemistry of melanocytic proliferations

CONTEXT

Histologic analysis allows accurate classification of most melanocytic lesions as benign or malignant. Only in a minority of lesions is it necessary to use other techniques as an aid in the diagnosis. Among them, most authors recommend immunohistochemistry.

OBJECTIVE

To describe how to apply immunohistochemistry to particular differential diagnoses and the potential pitfalls.

DATA SOURCES

Personal experience and review of literature.

CONCLUSIONS

There is no single marker, or combination thereof, that establishes an unequivocal diagnosis of melanoma or nevus. Thus it is necessary to carefully analyze the pattern of expression (patchy versus diffuse) and localization (maturation) in the context of morphologic standard features.

Melanocytes in nonlesional sun-exposed skin: a multicenter comparative study

BACKGROUND

There are limited data regarding melanocyte density and distribution on sun-exposed skin of the head and neck, in particular, comparing morphology (hematoxylin-eosin [H&E] staining) and immunohistochemistry (Melan-A staining) on formalin-fixed tissue. Furthermore, comparisons of melanocyte density between distinct geographic populations have not been made using these methods. This information would be useful for physicians who use histologic criteria to diagnose and treat lentigo maligna.

OBJECTIVE

We aimed to characterize the density and distribution of melanocytes using Melan-A and H&E stains on nonlesional sun-exposed skin of the face and neck, and compare the results between patients seen in Florida and Minnesota. We also aimed to quantify the presence and extent of features considered characteristic of melanoma in these noncancerous specimens of sun-damaged skin. The overall goal was to be able to provide this information to physicians who perform histopathologic interpretations of skin biopsy specimens to potentially prevent the overdiagnosis of melanoma.

METHODS

In all, 100 patients undergoing Mohs micrographic and reconstructive surgery for basal cell and squamous cell carcinoma were enrolled, 50 each at the two sites. Permanent tissue sections were prepared from sun-exposed skin without clinical lesions. Melanocyte density and distribution were quantified.

RESULTS

The overall median and 90th percentile, respectively, of melanocytes per high-power field was 9 and 14 on the H&E-stained sections and 11 and 19 on the Melan-A-stained sections. The means were 9.3 and 12.0, respectively (P < .001). There was evidence that melanocyte densities were higher in patients in Florida than in Minnesota, at least using H&E staining. There was evidence of lower melanocyte densities with increasing age, more so for Melan-A than H&E staining, and higher densities in men using Melan-A. Confluence was noted in 24% of cases using H&E and 45% using Melan-A. More than two thirds of these were classified as having mild confluence, whereas the others demonstrated higher amounts of confluence (3-8 melanocytes). Only 37 patients had a follicle present; of these, 7 patients had follicular extension although this did not extend beyond 1 mm in depth. Cytologic atypia was noted in 19 of the 100 patients; pagetoid spread was found in 3.

LIMITATIONS

This was a selected population of patients; results may not be generalizable to the wider population. Variables such as contours of the epidermis (rete density), density of hair follicles, and epidermal thickness may affect the reproducibility of the results. Melanomas were not included for comparison.

CONCLUSION

Relatively high melanocyte density, mild to moderate confluence of melanocytes, focal pagetosis, superficial follicular extension (<1.0 mm), and mild or moderate cytologic atypia may be observed in the absence of a melanocytic neoplasm. It is important for physicians to be aware of these findings so that such features are interpreted appropriately when making a histologic assessment that may ultimately influence therapy and outcome.

Use of immunohistochemistry in the diagnosis of melanocytic lesions: applications and pitfalls

The accurate diagnosis of melanocytic lesions is essential for the adequate clinical management of the patients. Besides the histopathologic examination, immunohistochemical studies are often used as an adjunct in distinguishing melanocytic lesions from tumors with different origin or between benign and malignant melanocytic lesions. In the first part of this article, we analyze data on currently used immunohistochemical markers, with special emphasis on their applicability to clinical practice, and underline their potential pitfalls. The pathogenesis of malignant transformation of melanocytes is not completely understood. Recent studies report that various melanoma progression markers are preferentially expressed in benign or malignant melanocytic lesions or show different expression in subsequent stages of tumor development. Furthermore, in recent years, emerging genetic studies suggest that there are distinctive patterns of chromosomal aberrations in different subtypes of melanoma that can be altered by newly developed targeted therapies. In the second part of our article, we will discuss the most significant progression markers in melanoma that can be detected by immunohistochemistry and their potential usefulness for diagnosis, prognosis, staging or as therapeutic targets.

Spreading pigmented actinic keratosis: a review

INTRODUCTION

Spreading pigmented actinic keratosis (SPAK) is a common, but uncommonly reported or appreciated, variant of classic actinic keratosis (AK). It can mimic different pigmented lesions, which may be benign (eg, solar lentigo) or malignant (eg, lentigo maligna).

OBJECTIVE

We sought to review current data and identify areas needing further research to establish diagnostic guidelines for SPAK and to increase awareness of this common entity.

METHODS

A literature search was performed in both PubMed and MEDLINE databases using the search terms "spreading pigmented actinic keratosis," "pigmented solar keratosis," "pigmented actinic," and "pigmented solar." Each article was retrieved, reviewed, and summarized.

RESULTS

SPAK is a rarely reported lesion that can be difficult to distinguish from other benign and malignant pigmented lesions, including seborrheic keratosis, melanoma in situ (lentigo maligna type), and lentigo maligna melanoma. Located mainly on sun-exposed areas and with a size greater than 1.5 cm, the lesion typically spreads laterally. Pathologically, the lesion resembles classic AK with increased basal melanization. The malignancy potential has not yet been elucidated but destructive therapies such as cryotherapy are recommended.

LIMITATIONS

Reports not yet published or not included in the comprehensive databases we used may exist that were not analyzed.

CONCLUSIONS

SPAK can be associated with adjacent melanoma in situ; therefore, its diagnosis merits increased suspicion for coexisting melanoma.

Melanoma Margin Assessment

Primary cutaneous melanoma is treated by excisional surgery and careful histologic assessment of the specimen margins is a crucial component of pathology reporting. Surgical margins may be assessed by conventional transverse (bread-loaf) vertical sections, by en face vertical sections, or by en face oblique sections. Transverse techniques only sample a small percentage of the surgical margin. En face techniques are technically challenging but allow assessment of close to 100% of the margin. Margin assessment for melanoma removed from chronically sun-damage skin is difficult. Melanoma in situ shows contiguous melanocyte growth, nesting, or intraepidermal pagetoid spread. Pitfalls include solar melanocytic hyperplasia, solar lentigines, melanocytic hyperplasia secondary to previous biopsy, lichenoid reactions, and invasive melanoma mimicking scar or benign nevus. En face sections can be used to assess margins for melanoma on sun-damaged skin, and evidence suggests that frozen sections may also be employed by experienced clinicians. Immunohistochemistry is a useful ancillary technique, enabling more accurate identification of in situ melanoma within a surgical margin.

Melan-a-positive "pseudomelanocytic nests": a pitfall in the histopathologic and immunohistochemical diagnosis of pigmented lesions on sun-damaged skin

We encountered recently 3 cases with a histopathologic diagnosis of melanoma in situ on sun-damaged skin (male = 2, female = 1; median age: 59 years; range: 52-60 years). The diagnosis was based mainly on the finding of actinic elastosis in the dermis and increased number of melanocytes in the epidermis and was confirmed by strong positivity for Melan-A in single cells and in small nests ("pseudomelanocytic nests"), located at the dermoepidermal junction. Indeed, examination of slides stained with hematoxylin and eosin revealed the presence of marked hyperpigmentation and small nests of partially pigmented cells at the dermoepidermal junction, positive for Melan-A. The histologic and especially the immunohistochemical features were indistinguishable from those of melanoma in situ on chronic sun-damaged skin. In addition, a variably dense lichenoid inflammation was present. Clinicopathologic correlation, however, showed, in all patients, the presence of a lichenoid dermatitis (phototoxic reaction, 1 case; lichen planus pigmentosus, 1 case; and pigmented lichenoid keratosis, 1 case). Our cases clearly show the histopathologic pitfalls represented by lichenoid reactions on chronic sun-damaged skin. Immunohistochemical investigations, especially if performed with Melan-A alone, may lead to confusing and potentially disastrous results. The unexpected staining pattern of Melan-A in cases like ours raises concern about the utility of this antibody in the setting of a lichenoid tissue reaction on chronic sun-damaged skin. It should be underlined that pigmented lesions represent a paradigmatic example of how immunohistochemical results should be interpreted carefully and always in conjunction with histologic and clinical features.

Surgical management of melanoma in situ on chronically sun-damaged skin

BACKGROUND

Lentigo maligna (LM) commonly presents as a slow-growing pigmented macular lesion in chronically sun-damaged skin and may progress to invasive melanoma. Many regard it as a subtype of melanoma in situ (MIS), and surgical excision remains the preferred treatment, but standard 5-mm surgical margins recommended for typical MIS are often insufficient for LM due to its indistinct borders both clinically and histologically.

METHODS

A search of the literature was conducted to review specialized surgical techniques for the treatment of LM, focusing on methods that employ total peripheral margin assessment prior to definitive closure, using either frozen or permanent histologic sections.

RESULTS

Many investigators have reported surgical modalities utilizing permanent sections for margin control, including variations of the "square" procedure and "perimeter" technique. Recurrence rates are low with these methods, but only short-term data have been reported. Similarly, several studies have demonstrated the efficacy of Mohs micrographic surgery (MMS) for treatment of MIS, with recurrence rates generally less than 1% over 3 to 5 years of follow-up. Many investigators have had success with immunohistochemical stains to identify melanocytes on frozen sections, aiding margin assessment in MMS.

CONCLUSIONS

Compared to standard excision, methods that employ surgical margin control offer superior cure rates for LM and should be utilized when available. Total peripheral margin assessment using staged excisions and permanent sections is a simple and effective alternative to MMS for institutions that lack the resources for intraoperative frozen section analysis.