Pathology: adamantinoma / osteofibrous dysplasia–like adamantinoma

Adamantinoma, classic

  • Nests and cords of epithelial cells set in fibrous stroma

  • Epitheliod cells with eosinophilic cytoplasm and desmosomes; ovoid nuclei with mild pleomorphism and inconspicuous mitotic activity

  • Intervening stroma composed of spindle cells with a loose fascicular pattern; cytoplasm is eosinophilic; nuclei are ovoid and monomorphic with inconspicuous mitotic activity

  • IHC: keratin (AE1/AE3), p40

  • Soft tissue extension

Adamantinoma, classic

  • Nests and cords of epithelial cells set in fibrous stroma

  • Squamoid epithelial cells with eosinophilic cytoplasm and desmosomes; ovoid nuclei with mild pleomorphism and inconspicuous mitotic activity

  • Intervening stroma composed of spindle cells with a storiform pattern; cytoplasm is eosinophilic; nuclei are ovoid and monomorphic with inconspicuous mitotic activity

  • Peripheral irregular bone trabeculae with conspicuous osteoblastic rimming

Adamantinoma, osteofibrous dysplasia-like

  • Inconspicuous tubules and individual epithelial cells set in fibrous stroma

  • Epithelial cells with scant eosinophilic cytoplasm; bland ovoid nuclei with inconspicuous mitotic activity

  • Prominent stroma composed of spindle cells with a storiform pattern; cytoplasm is eosinophilic; nuclei are ovoid and monomorphic with inconspicuous mitotic activity

  • Interspersed irregular bone trabeculae with conspicuous osteoblastic rimming

  • IHC: keratin (AE1/AE3)

Epithelial cells may be difficult to appreciate without the benefit of immunohistochemistry for keratin or p63

Adamantinoma, osteofibrous dysplasia-like

  • Inconspicuous tubules and individual epithelial cells set in fibrous stroma

  • Epithelial cells with scant eosinophilic cytoplasm; bland ovoid nuclei with inconspicuous mitotic activity

  • Prominent stroma composed of spindle cells with a storiform pattern; cytoplasm is eosinophilic; nuclei are ovoid and monomorphic with inconspicuous mitotic activity

  • Interspersed irregular bone trabeculae with conspicuous osteoblastic rimming

  • IHC: keratin (AE1/AE3), p63

Epithelial cells may be difficult to appreciate without the benefit of immunohistochemistry for keratin or p63