Cytologic diagnosis of papillary renal neoplasm with reverse polarity.

Background: Papillary renal neoplasm with reverse polarity is a recently recognized low-grade neoplasm with a favorable prognosis. To date, its cytologic features have not been well documented.
Methods: Two patients with papillary renal neoplasm with reverse polarity sampled by fine needle aspiration and core needle biopsy are described, one of whom is under active surveillance without clinical progression and the other is alive and well 16 years after partial nephrectomy.
Results: The cytologic features included a mix of papillae and dispersed cells with abundant oncocytic cytoplasm and round, bland nuclei apically displaced away from the papillary core. Immunohistochemistry showed positive staining for GATA3 in both cases. Molecular studies on one of the cases showed a KRAS p.G12V mutation.
Conclusions: The cytologic features of this distinctive, indolent neoplasm are important to recognize because patients with papillary renal neoplasm with reverse polarity may be excellent candidates for partial nephrectomy or even active surveillance.
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