Pathology: synovial sarcoma

Synovial sarcoma

  • Cellular; sheets and nests of polygonal cells and fascicles of spindle cells

  • Scant amphophilic cytoplasm

  • Round-ovoid nuclei with crowding, mild pleomorphism; mitotic activity

  • Wiry collagen interspersed between the cells; thin-walled, branching vessels; necrosis

  • RNA-seq: SS18::SSX2 gene fusion

Synovial sarcoma

  • Cellular; spindle cell fascicles

  • Eosinophilic cytoplasm with indistinct cell borders

  • Ovoid nuclei with striking palisading, mild pleomorphism; mitotic activity

  • Abundant necrosis

  • RNA-seq: SS18::SSX1 gene fusion

Synovial sarcoma

  • Cellular; spindle cell fascicles

  • Pale eosinophilic cytoplasm with indistinct cell borders

  • Ovoid nuclei with striking palisading, mild pleomorphism; mitotic activity

  • RNA-seq: SS18::SSX2 gene fusion

Synovial sarcoma

  • Cellular; biphasic; spindle-epithelioid cells in nests and fascicles with areas of gland formation

  • Abundant pale amphophilic cytoplasm

  • Plump ovoid nuclei with crowding, prominent nucleoli and mild pleomorphism; mitotic activity

  • Wiry collagen interspersed between the cells; thin-walled, branching vessels; necrosis

  • IHC: keratin (AE1/AE3)

  • RNA-seq: SS18::SSX2 gene fusion

Synovial sarcoma

  • Cellular; sheets-nests of polygonal cells

  • Scant pale amphophilic cytoplasm

  • Round-ovoid nuclei with mild pleomorphism; mitotic activity

  • Wiry collagen interspersed between the cells; prominent branching thin-walled vasculature

  • IHC: epithelial membrane antigen

  • RNA-seq: SS18::SSX2 gene fusion

Synovial sarcoma, biphasic

  • Cellular; biphasic; spindle cell fascicles with epithelioid gland formation

  • Abundant pale amphophilic cytoplasm

  • Plump ovoid nuclei with crowding, prominent nucleoli and mild pleomorphism; inconspicuous mitotic activity

  • Dystrophic calcification

  • RNA-seq: SS18::SSX1 gene fusion

Synovial sarcoma, biphasic

  • Cellular; biphasic; spindle cell fascicles with epithelioid gland formation

  • Abundant pale amphophilic cytoplasm

  • Ovoid-round nuclei with minimal pleomorphism; inconspicuous mitotic activity

  • RNA-seq: SS18::SSX1 gene fusion

Synovial sarcoma

  • Spindle cells with herringbone pattern

  • Amphophilic cytoplasm

  • Plump ovoid nuclei with crowding, mild pleomorphism; mitotic activity

  • Wiry collagen interspersed between the cells; occasional broad bands of collagen; focal myxoid stroma; prominent dystrophic calcification

  • RNA-seq: SS18:SSX1 gene fusion

Synovial sarcoma

  • Cellular; spindle cells with herringbone-storiform pattern

  • Scant amphophilic cytoplasm

  • Plump ovoid nuclei, minimal pleomorphism; mitotic activity

  • Focal myxoid stroma

  • RT-PCR: SS18::SSX gene fusion

Synovial sarcoma

  • Spindle-stellate cells with herringbone-fascicular pattern

  • Scant amphophilic cytoplasm

  • Hyperchromatic ovoid nuclei, minimal pleomorphism; inconspicuous mitotic activity

  • Myxoid stroma

  • RNA-seq: SS18:SSX2 gene fusion

Synovial sarcoma

  • Cellular; spindle cells with herringbone pattern

  • Minimal eosinophilic cytoplasm with long tapering processes

  • Elongated fusiform nuclei with mild pleomorphism; inconspicuous mitotic activity

  • Prominent wiry collagen interspersed between the cells

  • RT-PCR: SS18::SSX gene fusion

Synovial sarcoma

  • Spindle-ovoid cells with vague fascicular pattern

  • Pale eosinophilic cytoplasm with indistinct cell borders

  • Monomorphic ovoid nuclei; rare mitotic activity

  • Nodules of hyaline stroma (reminiscent of cartilage / osteoid)

  • RNA-seq: SS18:SSX2 gene fusion

Synovial sarcoma

  • Cellular; sheets-nests of round cells

  • Scant amphophilic cytoplasm

  • Round-ovoid nuclei with mild pleomorphism; mitotic activity

  • Prominent branching thin-walled vasculature

  • IHC: keratin (AE1/AE3)

  • RT-PCR: SS18::SSX gene fusion