DFSP


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  • Clinical

    • indurated plaques, nodules
    • site: trunk, proximal extremities, head/neck
    • superficial, low grade, locally aggressive (but rarely metastasize)
    • high recurrence rate
    • 10-15% progress to fibrosarcomatous DFSP
    • tx: wide excision (preferably 2-3 cm margin), imatinib

  • Histology

    • infiltrating dermis and subq, sparing epidermis
    • densely hypercellular, spindle cells, storiform/whirling
    • low grade cytology: minimal atypia or mitosis
    • honeycomb fat infiltration: tumor involves fibrous septa, interdigitating the fat cells

  • Variants

    • fibrosarcomatous DFSP: increased atypia and mitosis, reduced/loss of CD34, increased p53
    • pigmented DFSP (Bednar tumor): has pigmented cells
    • myxoid DFSP: myxoid, lots of vessels
    • DFSP with myoid differentiation
    • plaque like DFSP
    • giant cell fibroblastoma = juvenile, multinucleated giant cells lining vasculature

  • Molecular

    • COL1A1-PDGFB fusion
    • t(17;22)

  • Stains

    • positive: CD34
    • negative: desmin, S100, CK
    • can be weakly positive for EMA
    • fibrosarcomatous DFSP: reduced/loss of CD34 in half, increased p53
    • myoid differentiation stains SMA
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