American Urological Association - Myofibroblastic Lesion

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Home Education Educational Programs E-Learning Pathology for Urologists Urinary Bladder Mesenchymal and Other Tumors Myofibroblastic Lesion

Myofibroblastic Lesion

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  • Referred to in literature as inflammatory pseudotumor and pseudosarcomatous myofibroblastic proliferation.
  • Rare, typically patients are in their 20's to 50's.
  • Some may occur with history of prior bladder trauma or surgical instrumentation (post-operative spindle cell nodule).
  • Cystoscopy shows polypoid or submucosal nodule or mass 1.5 - 13 cm in size; those associated with prior bladder surgery are usually smaller.
  • A subset shows overexpression of ALK1, with associated chr 2p23 translocation (ALK gene) that can be detected by in situ hybridization.

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  • Histology:
    • Loose interlacing fascicles of spindle cells with elongated cytoplasmic processes (like myofibroblasts) (image A), (image B), (image C), & (image D).
    • Minimal nuclear atypia but may have increased mitotic activity.
    • Admixed inflammation and granulation type vascularity.
    • Tumor may extend deep into muscularis propria, but does NOT indicate malignancy.
  • Immunohistochemistry: keratin+ (like sarcomatoid carcinoma) and smooth muscle actin+ (like leiomyosarcoma).
  • DDX for sarcomatoid (spindle cell) urothelial carcinoma and leiomyosarcoma (both tumors are ALK1 negative).
  • May recur in about 10% of cases, but has no metastatic potential.

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