Clear Cell Papillary Renal Cell Carcinoma - An Indolent Subtype of Renal Tumor

Background: Clear cell papillary renal cell carcinoma (CCPRCC) is a new but rare tumor entity as listed in the World Health Organization 2016 renal tumor classification. Around 360 cases have been reported in the English literature to date, and only one tumor with sarcomatoid change was reported to develop distant metastasis. In the present study, we aim to review the clinical course and analyze the treatment outcome of CCPRCC in our institution.

Methods: We retrospectively collected patients diagnosed with CCPRCC between January 2008 and September 2016 in our institute. The clinical features, pathology slides, and clinical outcomes were reviewed.

Results: Twenty-five patients were collected during the study period, with a mean age at diagnosis of 62.8 years (range 35-85 years). Three patients developed the tumor in their native kidney following a kidney transplant, and three patients were diagnosed by needle biopsy before cryoablation therapy due to high surgical risk. The mean follow-up time was 49.7 months (range 12-119 months). During the follow-up period, all patients were alive without local recurrence or distant metastasis. All tumor specimens in our series expressed cytokeratin 7 (CK7) diffusely in immunohistochemistry staining. One patient was diagnosed with pT3a cN0M1, Fuhrman grade 3 CCPRCC with renal vein invasion and lung metastasis in 2010 on the basis of the histologic pattern and immunoreactivity for CK7. The clinical course was not compatible with any of the reported cases in the literature, so the kidney specimen was re-examined using whole-exome sequencing. The diagnosis was then revised to clear cell renal cell carcinoma.

Conclusion: Our series confirmed that CCPRCC has an indolent clinical behavior. When the diagnosis is made in a high-grade renal tumor, it should be carefully re-confirmed using cytogenetic or genomic methods.