Indian Journal of Pathology and Microbiology

: 2020  |  Volume : 63  |  Issue : 2  |  Page : 327--329

Oncocytic variant of papillary renal cell carcinoma: A rare or underreported entity?

Ashutosh Rath1, Wonchibeni T Murry1, Varuna Mallya1, Nita Khurana1, Sudhir Kumar Jain2,  
1 Department of Pathology, Maulana Azad Medical College, New Delhi, India
2 Department of General Surgery, Maulana Azad Medical College and Associated Lok Nayak Hospital, New Delhi, India

Correspondence Address:
Varuna Mallya
Department of Pathology, Maulana Azad Medical College, New Delhi

How to cite this article:
Rath A, Murry WT, Mallya V, Khurana N, Jain SK. Oncocytic variant of papillary renal cell carcinoma: A rare or underreported entity?.Indian J Pathol Microbiol 2020;63:327-329

How to cite this URL:
Rath A, Murry WT, Mallya V, Khurana N, Jain SK. Oncocytic variant of papillary renal cell carcinoma: A rare or underreported entity?. Indian J Pathol Microbiol [serial online] 2020 [cited 2020 Jul 14 ];63:327-329
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Papillary renal cell carcinoma (PRCC) is among the well-known malignant renal tumors, constituting 10%–15% of renal cell carcinomas (RCCs) and exhibits distinct clinical, pathological, and molecular features. It is morphologically further subclassified into type 1 and type 2 PRCC. Type 1 PRCC shows papillae lined by smaller cells in a single layer showing scant pale cytoplasm and small nuclei with inconspicuous nucleoli. The cores of the papillae often show numerous foamy histiocytes. Type 2 PRCC exhibits papillae lined by cells showing higher nuclear grade with pseudostratification and abundant eosinophilic cytoplasm. This morphological distinction is important prognostically as well, since type 2 PRCC has a poorer prognosis.[1],[2] Recently, another type of PRCC has been recognized with features overlapping between type 1 and type 2 PRCCs with the cells showing prominent oncocytic changes. This novel variant has been named as oncocytic variant of PRCC (OPRCC).[3]

A 67-year-old male presented with pain in the left flank for 6 months, with a left renal mass in the midregion measuring 5 × 3 × 3 cm picked up on computed tomography of the abdomen. A left simple nephrectomy was performed and the specimen was sent for histopathological examination. The kidney showed a solid-cystic brownish mass in the middle region measuring 6 × 3.5 × 3.5 cm. The mass showed areas of hemorrhage and exhibited focal extension into the perinephric fat with capsular invasion [Figure 1]. On microscopy, the mass showed a tumor comprising predominantly of papillae lined by tumor cells exhibiting abundant granular eosinophilic cytoplasm [Figure 2]a. The core of the papillae focally showed foamy histiocytes [Figure 2]b. The tumor cells showed considerable variations in the nuclear characters. Many of the areas showed smaller single layer of nuclei [Figure 2]c, while other areas showed larger, Fuhrman grade 2 nuclei with pseudostratification [Figure 2]d. Focal areas showed nuclei arranged at the periphery of the cell with a reverse polarity [Figure 2]e. Areas of hemorrhage were noted. Many of the tumor cells showed hemosiderin deposition as highlighted by Perls stain [Figure 2]f. Focally, the tumor cells showed clear cell change [Figure 2]g. No necrosis or increased mitoses were noted. The tumor was involving the renal sinus and infiltrating into the perirenal fat. Renal hilar vessels and the ureteric margin were free of tumor. The adjacent uninvolved kidney showed features of chronic pyelonephritis. On immunohistochemistry, the tumor cells were positive diffusely for vimentin [Figure 2]h and CD10 [Figure 2]i, while they were negative for CD117 and CK7. The patient was lost to follow-up.{Figure 1}{Figure 2}

First described by Lefevre et al. in 2005 and now mentioned in the 2016 WHO classification of renal tumors, OPRCC shows overlapping features of type 1 and type 2 PRCC.[3],[4] It usually occurs in older adults with the mean age ranging from 56 years to 71 years in various studies and shows male preponderance.[1],[3],[5] Grossly, most of the studies mention a unifocal tumor limited to the kidney.[1],[3] However, the present case showed infiltration of the tumor into the perirenal fat and involvement of the renal sinus. Histologically, the tumor shows a predominant papillary pattern with the tumor cells showing abundant granular eosinophilic cytoplasm akin to an oncocyte with variably sized nuclei. Focal areas show nuclear pseudostratification, while other areas may show single layering.[5] Studies have found the tendency of the nuclei to be arranged at the periphery of the cell with inverse polarity, a feature exhibited in the present case as well, so also focal cells showing clear cytoplasm is mentioned.[5],[6] Another characteristic feature described is the hemosiderin-laden tumor cells which were also seen in the present case.[5] Immunohistochemical analysis of OPRCC shows diffuse positivity for Alpha-methylacyl-CoA racemase (AMACR), vimentin, and CD10. We could not test AMACR in the present case. CD117 is usually negative in OPRCC. Immunoreactivity for CK7 is observed in 50%, CK19 in 65%, E-cadherin in 50%, and RCC antigen in 50% of cases. CK7 usually shows uniform and strong positivity in type 1 and most of the type 2 PRCCs. Epithelial membrane antigen (EMA) is shown to be either negative or only weakly positive. Progesterone receptor is found to be negative in OPRCC. Hes et al. found only 33% of their cases of OPRCCs (12 cases) to be positive for parvalbumin. Ki-67 index is usually very low.[1],[3],[5] Most of the cases are immunopositive for Mesenchymal Epithelial transition (MET) with the molecular study, like fluorescent in situ hybridization assay, showing trisomy of chromosomes 7 and 17, and loss of chromosome Y. Karyotyping has shown loss of chromosomes 1, 14 and Y and trisomy 3.[5] The patients are described to show an indolent course.[6] The closest differential diagnosis is renal oncocytoma especially when there are solid areas of OPRCC and differentiating them is important as OPRCC is a malignant tumor. Oncocytoma shows only focal papillary features, is CD117 and progesterone receptor positive, and is negative for AMACR, vimentin, and CD10.[1] Other differential diagnoses include eosinophilic variant of chromophobe RCC which does not show papillary architecture and oncocytoma-like angiomyolipoma which shows immunoreactivity for HMB45.[1]

Many of the studies on OPRCC are case series showing variable features. The present case shows a good amalgamation of many of the features mentioned, in a single case, making it an interesting incident. It is not clear if OPRCC is an independent type of carcinoma or if it represents a subtype of PRCC. 2016 WHO classification of renal tumors recommends characterizing such tumors as type 2 PRCC till sufficient data are available. However, distinction from type 2 PRCC is important as OPRCCs may have a better prognosis.

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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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2Jagtap SV, Beniwal A, Jagtap SS, Huddedar A. Papillary renal cell carcinoma type-II: A distinct clinicopathological subtype of renal epithelial neoplasm. Ann Path Lab Med 2016;3:279-82.
3Lefevre M, Couturier J, Sibony M, Bazille C, Boyer K, Callard P, et al. Adult papillary renal tumor with oncocytic cells: Clinicopathologic, immunohistochemical, and cytogenetic features of 10 cases. Am J Surg Pathol 2005;29:1576-81.
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