Diagnostic Utility of Neural Stem and Progenitor Cell Markers Nestin and SOX2 in Distinguishing Nodal Melanocytic Nevi From Metastatic Melanomas

Pei-Ling Chen; Wei-Shen Chen; Jianping Li; Anne C Lind; Dongsi Lu

Disclosures

Mod Pathol. 2013;26(1):44-53. 

In This Article

Abstract and Introduction

Abstract

Sentinel lymph node evaluation is a critical component of melanoma staging, and lymph node status provides one of the most powerful predictors of melanoma recurrence and survival. One of the well-known diagnostic pitfalls in melanoma sentinel lymph node evaluation is the presence of nodal melanocytic nevi, which has been demonstrated in up to 26% of lymphadenectomy specimens and specifically in melanoma patients. Melanocytic markers enhance the sensitivity of melanoma detection in sentinel lymph nodes. However, established markers such as anti-melan-A/MART1, S100 protein and SOX10 antibodies cannot discriminate melanoma metastasis from nodal nevi. Recent studies have demonstrated strong expression of neural stem/progenitor cell markers nestin and SOX2 in melanoma. In this study, we tested the diagnostic utility of nestin and SOX2 in differentiating metastatic melanomas from nodal nevi. Twenty-three lymph nodes with metastatic melanomas and 17 with nodal nevi were examined. Of the 23 metastatic melanomas, 18 showed diffuse and strong (3+) nestin, 4 showed rare cells with strong (3+) nestin, and one showed diffuse but faint (1+) nestin staining. Nuclear SOX2 was positive in 13 metastatic melanomas. In contrast, 15 nodal nevi showed no nestin, and 2 showed rare cells with very faint (<1+) nestin staining. SOX2 was negative in 13 nodal nevi. Overall, nestin was strongly expressed in metastatic melanomas (n=22/23; 96%), but not in nodal melanocytic nevi (n=15/17; 88%; P<0.0001). SOX2 was also expressed in metastatic melanomas (n=13/23; 57%) but not in the majority of nodal melanocytic nevi (n=13/16; 81%; P=0.02). In one lymph node harboring metastatic melan-A-negative desmoplastic melanoma, nestin and SOX2 strongly highlighted the infiltrating tumor cells, suggesting the potential clinical value of these two markers in desmoplastic melanoma lymph node biopsies. This study provides evidence that nestin and SOX2 can effectively differentiate nodal melanocytic nevi from metastatic melanomas and serve as powerful diagnostic adjuncts in melanoma staging.

Introduction

Malignant melanoma is a malignant tumor of melanocytes that accounts for less than 10% of all skin cancer diagnoses but the majority of skin cancer-related deaths.[1] For patients diagnosed with malignant melanoma, sentinel lymph node biopsy is an essential component of tumor staging, and lymph node status provides one of the most powerful predictors of melanoma recurrence and survival.[2–4] When melanoma metastasizes, a regional lymph node is the most common site, and tumor burden can range from rare tumor cells to complete effacement of lymph nodes. The presence of either micro- or macrometastasis in a single lymph node changes melanoma staging from stage I to stage III.[5] In addition, a single positive lymph node signifies a decrease in 10-year survival from 95% (stage IA) to 68% (stage IIIA), and with more than three positive lymph nodes, 10-year survival rate drops to 24%.[5] Although controversial, many surgeons perform completion lymphadenectomy based on the histological diagnosis of a single positive sentinel lymph node,[2] and high-dose interferon-α2b is offered as an adjuvant treatment option for stage III melanoma. As sentinel lymph node evaluation carries significant prognostic and therapeutic implications, accurate assessment of sentinel lymph node biopsies is crucial for appropriate tumor staging and patient management.

The recently published seventh edition of the AJCC staging system for cutaneous melanoma has incorporated two important changes specific to the handling and interpretation of sentinel lymph node biopsies.[5] First, unlike breast cancer, there is no lower threshold of tumor burden to define regional nodal metastasis, reflecting the view that even small tumor volume in lymph nodes may be clinically significant.[6] Second, for the purpose of melanoma staging, nodal micrometastasis is now defined using either H&E or immunohistochemical staining, which must include at least one melanocyte-specific marker. These two changes in AJCC tumor staging herald more prevalent use of immunohistochemical markers for the detection of melanoma micrometastasis and an increased likelihood of encountering challenging nodal melanocytic lesions due to more sensitive detection methods.

One of the major diagnostic pitfalls in sentinel lymph node biopsies from melanoma patients is the presence of nodal melanocytic nevi.[7,8] Benign melanocytic nevi are reportedly identified in 8–26% of lymphadenectomy specimens and occur more frequently in melanoma patients, specifically in sentinel lymph nodes.[8] Histologically, nodal melanocytic nevi consist of aggregates of cytologically bland melanocytes that reside in the lymph node capsule and trabeculae, whereas metastatic melanomas are predominantly subcapsular, sinusoidal and intraparenchymal, and show cytological features of malignancy.[9] Nonetheless, as melanomas often display a wide spectrum of cytological features and can be morphologically bland, as in nevoid melanoma, the distinction between benign nodal nevi and melanoma metastases can be difficult. To complicate the matter further, both metastatic melanomas and nodal melanocytic nevi can occupy unusual sites within the lymph nodes. It has been shown that melanoma cells can seed lymph node capsules,[10] and nevoid aggregates have been identified in the subcapsular space and even within nodal parenchyma,[7] mimicking metastasis. On the basis of morphological criteria alone, distinguishing nodal melanocytic nevi from nodal melanomas can be very difficult, especially when the melanocytic focus in question is small and lacks overt cytological atypia. In such histologically ambiguous lesions, care must be taken to avoid over-diagnosing nodal nevi as metastatic melanomas or under-diagnosing tumor deposits as nodal melanocytic nevi.

Many melanocytic markers are routinely used in the evaluation of microscopic metastasis, yet no single immunostain is adequately specific in differentiating melanoma metastases from nodal melanocytic nevi.[11] Melan-A/MART1 and SOX10 are highly sensitive for melanoma.[12,13] However, they indiscriminately highlight melanoma and nevus cells, and cannot distinguish between these two entities.[13,14] HMB-45 is an antibody directed against glycoprotein gp100 in premelanosomes, yet it is also positive in isolated or aggregated melanophages in sentinel lymph nodes.[15] S100 protein, one of the most sensitive markers for melanoma, is also expressed in nodal melanocytic nevi and diffusely highlights dendritic cells,[14,16] making the interpretation of this marker particularly confusing in lymph node specimens.

With the recent isolation of tumorigenic stem cells in human,[17] we postulated that even though metastatic melanomas and nodal melanocytic nevi share common lineage, melanomas are more likely to express neural stem/progenitor cell markers than nodal melanocytic nevi, which are presumably terminally differentiated cells. A few studies have demonstrated that the neural stem/progenitor cell marker nestin, a type VI intermediate filament transiently expressed in early migrating and proliferating neuroectodermal cells,[18] is expressed in primary and metastatic melanomas.[19–23] Furthermore, this expression seem to correlate with more advanced disease and decreased 5-year survival.[24,25] In contrast, the majority of melanocytic nevi, even dysplastic nevi, showed no or weak nestin staining.[20,23] SOX2, or SRY (sex determining region Y)-box 2, is a transcription factor expressed by neural progenitor cells throughout the vertebrate CNS, and can bind to and regulate the nestin core enhancer.[26] It is also one of the key transcription factors essential for the induction of pluripotent stem cells from fibroblasts in mice.[27] Recently, it has been shown on whole tissue sections that metastatic melanomas expressed both nestin and SOX2, but no cutaneous melanocytic nevi were positive for both markers.[23]

The aim of this study was to investigate the diagnostic utility of neural stem/progenitor cell markers nestin and SOX2 in differentiating nodal melanocytic nevi from metastatic melanomas.

Comments

3090D553-9492-4563-8681-AD288FA52ACE

processing....