Clear Cell Papillary Renal Cell Carcinoma: A Potential Mimic of Conventional Clear Cell Renal Carcinoma on Core Biopsy

Abstract

Clear cell papillary renal cell carcinoma (CCP-RCC) is a recently described, relatively uncommon variant of renal cell carcinoma (RCC) with a reported incidence of 4.1%. Thought to only arise in those with end stage renal disease, CCP-RCC is increasingly identified in those without renal impairment. CCP-RCCs have unique morphologic, genetic, and immunohistochemical features distinguishing them from both conventional clear cell renal cell carcinomas and papillary renal cell carcinomas. Immunohistochemically, these tumors are positive for CK7 and negative for CD10 and racemase. This is in contrast to conventional cell renal cell carcinomas (CK7 negative, CD10 positive) and papillary cell carcinomas (CK7, CD10, and racemase positive). These tumours appear to be indolent in nature, with no current documented cases of metastatic spread. We present the case of a 42-year-old female who presented with an incidental finding of a renal mass that on a core biopsy was reported as clear cell carcinoma, Fuhrman grade 1. She subsequently underwent a radical nephrectomy and further histological examination revealed the tumor to be a clear cell papillary renal cell carcinoma, Fuhrman grade 1.

Early-stage clear cell tubulopapillary renal cell carcinoma: imaging features and distinction from clear cell and papillary subtypes

“…Several imaging features trended towards statistical significance, but pair-wise analyses did not reveal a statistical significant difference ( 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 to the more common clear cell and papillary subtypes, CCTPRCC is considered an indolent cancer and may be appropriate to observe rather than treat in selected patients [4,11].…”

“…The presence of two of these features increases the specificity for differentiating between CCTPRCC and pRCC, but the increased specificity comes at the cost of lowering the sensitivity. The finding that CCTPRCC cannot be differentiated from ccRCC is supported by several pathology studies that have described CCTPRCC as a mimicker of ccRCC [1][2][3]11]. For example, pathologists may have difficulty distinguishing CCTPRCC from ccRCC with a low Fuhrman grade [1,2,4], and rely on immunohistochemistry to render the correct diagnosis [1-4, 7-9, 11, 24].…”

“…CCTPRCC is a recently recognized subtype of renal cell carcinoma [1,2] that has gross morphologic and histologic features which overlap with both ccRCC and pRCC [1][2][3][4][5][6][7][8][9]11]. In the radiology literature, CCTPRCC has been considered among atypical pRCC subtypes [13], and to our knowledge, the imaging features of this recently described RCC subtype have not been described.…”

“…To our knowledge, metastases have not been reported [1][2][3][4][7][8][9][10][11]. Therefore, the prospective differentiation of CCTPRCC from the more common subtypes such as clear cell RCC (ccRCC) and papillary RCC (pRCC) at an early stage may be useful for counseling patients on prognosis and treatment plans.…”

“…Among these, both CCTPRCC and ccRCC more frequently demonstrated nonenhancing areas than pRCC (p=0.0003 and 0.0006 respectively) (Fig. 4), but there was no difference in the frequency of nonenhancing areas between CCTPRCC and ccRCC (p=0.990).Several imaging features trended towards statistical significance, but pair-wise analyses did not reveal a statistical significant difference ( 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 to the more common clear cell and papillary subtypes, CCTPRCC is considered an indolent cancer and may be appropriate to observe rather than treat in selected patients [4,11].This study suggests that early stage CCTPRCC can be distinguished from pRCC based on a lower mean attenuation value on unenhanced CT, high signal on T2-weighted images, an illdefined margin, and more frequent nonenhancing areas. Specifically, a threshold unenhanced attenuation of 25 HU was found to be statistically significant for differentiating CCTPRCC from pRCC.…”