Cytopathologic features of clear cell papillary renal cell carcinoma: A recently described variant to be considered in the differential diagnosis of clear cell renal epithelial neoplasms

BACKGROUND: Clear cell papillary renal cell carcinoma (CCPRCC) is a distinctive variant of renal cell carcinoma that has been formally adopted by the new Word Health Organization classification. An emerging consensus has documented its particularly indolent course and emphasized its separation from conventional clear cell renal cell carcinoma (CCRCC) for treatment planning. CCPRCC features in cytologic preparations have not been studied. METHODS: This study retrospectively identified a series of CCPRCCs that had cytology samples before the histopathologic diagnosis and reviewed corresponding cytologic materials, including aspirate smears, cell block materials, touch preparations, and core biopsy samples. The identified clinicopathologic and cytologic features were tabulated. RESULTS: Five cases of CCPRCC with cytopathologic materials were identified from 4 women and 1 man aged 34 to 70 years (2 with end-stage renal disease), and the sampled lesions were 1.8 to 11.0 cm. The original cytopathologic diagnostic considerations ranged from atypical cyst-lining cells to angiomyolipoma to CCRCC and CCPRCC. The aspirate and touch preparation samples showed scant cellularity with scattered sheets and clusters of small, bland epithelial cells (much smaller than admixed renal tubular cells) with optically clear cytoplasm (lacking conspicuous cytoplasmic vacuolization) and small, grade 1 nuclei. The cell block materials and the core biopsy samples showed cyst walls with prominent myomatous stroma lined by low-grade epithelium with optically clear cytoplasm, inverse nuclear polarization, and a characteristic cytokeratin 7–positive/carbonic anhydrase IX–positive phenotype. Three cases were treated with resection, 1 case was treated with ablation, and 1 case was under surveillance. CONCLUSIONS: CCPRCC demonstrates recognizable cytomorphologic features and merits consideration in the cytologic differential diagnosis for kidney lesions. With increasing experience, more conservative management may be contemplated. Cancer Cytopathol 2016;124:565-72.