Emerging clinical applications of selected biomarkers in melanoma

Abstract

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.

Keywords: BRAFV600E; histone marks; immunohistochemistry; melanocytic differentiation.

Figure 1

MiTF accurately enumerates the melanocytes in the epidermis of chronic sun exposed skin and in lesions of lentigo maligna. Notes: (A) Chronic sun-damaged skin with atrophic epidermis and solar elastosis (*) with background increase in melanocytes along the dermal–epidermal junction (DEJ) (arrows) (H&E stain, ×100); (B) MiTF labels nuclei of melanocytes and allows for better enumeration of melanocytes along the DEJ (IHC stain, ×100); (C) Area of lentigo maligna with atypical melanocytes with back-to-back nuclei and pagetoid spread highlighted by MiTF (IHC stain, ×100). Abbreviations: H&E, hematoxylin and eosin; IHC, immunohistochemistry.

Figure 2

Evaluation of bread-loafed cross-sections of peripheral margins allows for comparison of the background increased density of melanocytes, reflective of chronic sun damage (at the periphery), with area of lentigo maligna (at the center).

Figure 3

Sox10 identifies rare tumor cells in heavily regressed areas of melanoma. Notes: (A) Melanoma nodule with extensive regression with melanophages (H&E stain, ×40); (B) Sox10 labels nucleus (arrows) of scattered viable melanoma cells in the regressed nodule with an absence of labeling in pigmented macrophages (IHC stain, ×400). Abbreviations: H&E, hematoxylin and eosin; IHC, immunohistochemistry.

Figure 4

Detection and confirmation of lymphovascular invasion. Notes: (A) Cluster of melanoma cells in a vascular-like space (*) (H&E stain, ×400); (B) D2-40 highlights lymphatic vessel and confirms LVI (IHC stain, ×400); (C) Dual IHC stain with MiTF (brown, nuclear) and D2-40 (red, cytoplasmic) highlights isolated melanoma cell in lymphatic channel (arrow) (×400); (D) Dual IHC stain with Sox10 (red, nuclear) and D2-40 (brown, cytoplasmic) confirms the collection of inflammatory cells (arrow) in a lymphatic vessel (arrow) and the absence of LVI (×400). Note the adjacent Sox10-positive melanoma cells. Abbreviations: H&E, hematoxylin and eosin; IHC, immunohistochemistry; LVI, lymphovascular invasion.

Figure 5

Detection of mitotic figures and G2+ tumor nuclei with histone markers. Notes: (A and C) Detection of mitotic figure(s) with PHH3 and H3KT (anti-H3K79me3TH80ph) (IHC stain, ×400); (B) Dual IHC stain with Mart1 (red, cytoplasmic) and PHH3 (brown, nuclear) confirms mitotic figure in melanoma cell (×400); (C) Mitotic figure highlighted with H3KT in Merkel cell carcinoma (MCC) (IHC stain, ×400); (D) G2+ tumor nuclei detected by H3KT in MCC (IHC stain, ×400). Abbreviation: IHC, immunohistochemistry.

Figure 6

Immunohistochemcial evaluation of BRAFV600E mutation status in melanoma. Notes: (A) Melanoma cells with diffuse, cytoplasmic labeling with anti-BRAFV600E (IHC stain, chromagen AEC, ×400); (B) Focal labeling of melanoma cells with anti-BRAFV600E and the presence of tumor heterogeneity in a subset of tumors (IHC stain, chromagen AEC, ×400); (C) Melanoma cells with notable melanin pigment (H&E stain, ×400); (D) Melanoma cells negative for anti-BRAFV600E; Brown color in cytoplasm of melanoma cells is melanin pigment (*) and not DAB chromagen (IHC stain, DAB, ×400). Abbreviations: AEC, 3-amino-9-ethylcarbazole; DAB, diaminobenzidine; H&E, hematoxylin and eosin; IHC, immunohistochemistry.

Figure 7

Immunohistochemcial evaluation of BAP-1 and BRAFV600E status in melanocytic lesions. Notes: (A) Melanocytic nevus composed of sheets of epithelioid-shaped melanocytes in the dermis (H&E stain, ×400); (B) Anti-BAP-1 demonstrates loss of nuclear expression in melanocytes (arrows) indicative of the presence of BAP-1 mutation (IHC stain, ×400); (C) Diffuse cytoplasmic expression of anti-BRAFV600E (IHC stain, ×400). Abbreviations: H&E, hematoxylin and eosin; IHC, immunohistochemistry.