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Papillary Adenoma

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  • Small epithelial tumor with papillary and/or tubular growth that is not >0.5 cm in size (those larger becomes papillary RCC, usually type 1).
  • Common incidental finding, seen in 7% of nephrectomies and higher in chronic renal disease with acquired cystic disease (~35%).
  • Cytogenetics: Contains chr +7 and +17 and -Y similar to papillary RCC.
  • Gross: White to tan solid nodules but frequently microscopic tumors can easily be overlooked (unless you really spend your time and looking close-up).
  • Histology:
    • Closely packed bland cells with scant basophilic and sometimes eosinophilic cytoplasm forming tubules and papillary structures (image A), (image B), (image C) & (image D).
    • Low-grade nuclei with no mitosis.
    • Lacks capsule and merges with the normal tubules.
    • Caveat: Any clear cell neoplasm in the cortex, even <0.5 cm, should not be considered adenoma (small clear cell RCC).

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  • Immunohistochemistry: CK7+ and AMACR+ like papillary RCC.
  • Benign outcome.
  • DDX: Main difference from RCC papillary type 1 (basophilic cytoplasm) and type 2 (eosinophilic cytoplasm) is small size and lack of capsule.
  • Possibility as precursor lesion for papillary RCC is being questioned partly because of the disparity in incidence of these two lesions.