Which histologic findings are characteristic of pleural synovial sarcoma?

Updated: Dec 25, 2019
  • Author: Joseph F Tomashefski, Jr, MD; more...
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Histologically, synovial sarcoma of the pleura resembles its soft-tissue counterpart. Indeed, it may be difficult if not impossible to clearly differentiate between pleural sarcomatoid mesothelioma and pleural synovial sarcoma by hematoxylin-eosin staining, conventional immunohistochemistry markers, and transducin-like enhancer of split 1 (TLE-1) labeling. [63]

Monophasic synovial sarcoma is more common than biphasic synovial sarcoma in the pleura. The monophasic variant is composed of densely packed short spindle cells, with a high nuclear-to-cytoplasmic ratio, arranged in interweaving fascicles. A hemangiopericytomatous pattern and/or hyaline fibrosis (with or without calcification) are common features. Frequent stromal mast cells are characteristic of synovial sarcoma.

The mitotic rate varies but is frequently brisk. Biphasic synovial sarcoma includes a spindle cell component as in the monophasic variant in addition to larger epithelial cells that are round to oval with pale cytoplasm and vesicular nuclei. Epithelial cells may be arranged in cords, nests, sheets, or acinar structures that may contain neutral intraluminal mucin. [64, 65]

Pathology of nonmesothelial cancers of the pleura. Pathology of nonmesothelial cancers of the pleura. Monophasic synovial sarcoma showing interlacing fascicles of spindle cells.
Pathology of nonmesothelial cancers of the pleura. Pathology of nonmesothelial cancers of the pleura. Higher magnification of neoplastic spindle cells. Note also round mast cells with granular cytoplasm (center of image).

A poorly differentiated variant of synovial sarcoma has also been described in which pleomorphic cells having a high mitotic rate and areas of necrosis may appear as spindle cells in a herringbone pattern, small cells, or large epithelioid cells. Whether biphasic or monophasic, poor cytological differentiation has been said to be associated with poor prognosis. [66]

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