Clear cell sarcoma in unusual sites mimicking metastatic melanoma

Abstract

Background: Clear cell sarcoma is an aggressive rare malignant neoplasm with morphologic and immunohistochemical similarities to malignant melanoma. Both disease entities display melanin pigment and melanocytic markers, making differentiation between the two difficult. Although clear cell sarcoma cases in the literature have mainly involved deep soft tissues of the extremities, trunk or limb girdles, we report here two cases of primary clear cell sarcoma in unusual sites and describe their clinicopathologic findings.

Case summary: The first case involves a 37-year-old female, who presented with jaw pain and a submandibular mass. The second case involves a 33-year-old male, who presented with back pain and a thoracic spine tumor. Both cases showed tumors with diffuse infiltration of neoplastic cells that were positive for melanocytic markers, and in both cases this finding led to an initial diagnosis of metastatic melanoma. However, further analysis by fluorescence in situ hybridization (commonly known as FISH) showed a rearrangement of the EWS RNA binding protein 1 (EWSR1) gene on chromosome 22q12 in both patients, confirming the diagnosis of clear cell sarcoma.

Conclusion: Distinction between clear cell sarcoma and malignant melanoma can be made by FISH, particularly in cases of unusual tumor sites.

Keywords: Case report; Clear cell sarcoma; Fluorescence in situ hybridization; Melanoma; Salivary gland; Spine.

Figure 1

Histopathology of the submandibular gland mass in Case 1. A: Section of the mass showed nests of poorly differentiated tumor cells infiltrating into the benign acinic cells (HE, × 50); B: Neoplastic cells displayed pleomorphic, bizarre nuclei with prominent nucleoli and mitotic figures (HE, × 400). HE: Hematoxylin and eosin.

Figure 2

Immunohistochemistry of the submandibular mass in Case 1. A-C: The tumor cells demonstrated positive staining for (A) Human Melanoma Black-45 (× 400) and (B) S-100 (× 400) and negative staining in neoplastic cells for (C) keratin (× 400); D: The melanin pigment in the tumor cells showed positive reaction to Masson Fontana stain (× 400).

Figure 3

Radiology and pathology of the thoracic paraspinal mass in Case 2. A: Magnetic resonance imaging of the tumor showed an enhancing thoracic spine mass involving the paraspinal soft tissues; B: Sections of the mass showed fascicles and nests of spindle cells (HE, × 50); C, D: Neoplastic cells displayed melanin pigments (HE, × 400) and positivity for Human Melanoma Black-45 by immunohistochemistry (× 400). HE: Hematoxylin and eosin.

Figure 4

Fluorescence in situ hybridization analysis of the spinal tumor in Case 2. Fluorescence in situ hybridization using a dual-color, break-apart probe for EWSR1 demonstrated one normal fusion (yellow) along with an extra red signal and extra green signal, indicating translocation.