borderline serous tumor


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  • Histology

    • architecture
      • hierarchical branching: progressively smaller branches terminating in tufts
      • if has only focal micropapillary, then sign out as borderline tumor with focal micropapillary features
      • can have papillary area mimicking LG serous carcinoma, but < 5mm and no atypia
    • lining: cilia, hobnailing, minimal atypia
    • stroma
      • microinvasion = pink cells in stroma with abundant cytoplasm, < 5mm, less ER/PR, lower Ki67, thought to be senescent cells
      • microinvasive carcinoma = atypia on par with low grade serous carcinoma

  • Implants

    • Non-invasive
      • epithelial type: no desmoplasia
      • desmoplastic type: stroma has desmoplasia
      • High risk features: small solid nests of cells surrounded by a space, micropapillae or cribriform growth
    • Invasive (into underlying tissue, not just stroma of implant)
    • High risk features and invasive implants behave like low grade serous carcinoma

  • Stains

    • positive: AE1AE3, EMA, BerEP4, WT1, PAX8, ER, PR
    • negative for diffuse p16 or mutated p53

  • Molecular

    • KRAS, BRAF mutation in 50%
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