Primary Clear Cell Sarcoma of the Dermis Mimicking Malignant Melanoma

Abstract

Background: Clear cell sarcoma is a rare malignant soft tissue neoplasm that typically involves tendons and aponeurosis. Clear cell sarcoma in the dermis is an extremely rare occurrence, and it is difficult to differentiate between this neoplasm and dermal malignant melanoma because they have similar morphologic and immunohistochemical features. Although rare, clear cell sarcoma of the skin typically occurs in the extremities. To our knowledge, there are no reported cases of primary clear cell sarcoma of the skin occurring in the neck. Here, we report an unusual case of clear cell sarcoma arising in the skin of the neck.

Case report: A 43-year-old female presented with a right neck lesion. Histologic sections of the lesion showed a nodular proliferation of spindle cells with pale cytoplasm with epithelioid features involving the entire dermis with no epidermal component. The tumour cells were positive for melanocytic markers, including S100 and Human Melanoma Black 45, which led to an initial diagnosis of malignant melanoma. Fluorescence in situ hybridization showed a rearrangement of the EWSR1 gene on chromosome 22q12, which led to a diagnosis of primary clear cell sarcoma in the skin.

Conclusion: Because the treatments for clear cell sarcoma and conventional melanoma are different, fluorescence in situ hybridization for EWSR1 should be performed in any dermal lesions with melanocytic features that do not have an in situ component.

Keywords: Clear cell; dermis sarcoma.; melanoma.

Figure 1. Histopathological examination of the skin. Sections show (a) diffuse infiltration of the dermis with sheets of neoplastic cells (b) without the involvement of the epidermis H&E x40 and x100 magnification respectively.

Figure 2. Histologic examination and immunohistochemical staining of the tumour. Higher magnification shows (a) nests and fascicles of spindle cells with clear cytoplasm and (b) wreath-like giant cells H&E x40 magnification. The tumour cells were positive for (c) S-100 and (d) HMB-45 (x400 magnification).

Figure 3. Fluorescence in situ hybridization analysis of the mass. The normal pattern consists of a fusion of the orange and green signals, while the rearranged EWSR1 is seen as a split of the fusion signal into red 5’ centromeric region and green 3’ telomeric region (LSI EWSR1 Dual Color Break Apart Probe).