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Peer Reviewed

Tumors

Renal Oncocytoma Mimicking Renal Cell Carcinoma

Volume 61 - Issue 8 - August 2021

AUTHORS:
Olubunmi Oladunjoye, MD, MPH1 • Adeolu Oladunjoye, MD, MPH2 • Anish Paudel, MD1 • Ronald Herb, DO1

AFFILIATIONS:
1Department of Internal Medicine, Tower Health Reading Hospital, West Reading, Pennsylvania
2Department of General Pediatrics, Division of Medical Critical Care, Boston Children’s Hospital, Boston, Massachusetts

CITATION:
Oladunjoye O, Oladunjoye A, Paudel A, Herb R. Renal oncocytoma mimicking renal cell carcinoma. Consultant. 2021;61(8):e38-e40. doi:10.25270/con.2020.11.00009

Received July 17, 2020. Accepted October 25, 2020. Published online November 9, 2020.

DISCLOSURES:
The authors report no relevant financial relationships.

ACKNOWLEDGEMENT:
We thank the Department of Pathology at Tower Health Reading Hospital for the histology images.

CORRESPONDENCE:
Olubunmi Oladunjoye, MD, Department of Internal Medicine, Reading Hospital, 420 S 5th Ave, West Reading, PA 19611 (olubunmi.oladunjoye@towerhealth.org)

 

A 61-year-old woman with a history of bladder prolapse and normal kidney function developed complications after a recent laparoscopic sacral colpopexy for urinary incontinence. Computed tomography (CT) scans revealed an incidental finding of an enhancing 3.3-cm mass within the right posterior kidney that was concerning for renal cell carcinoma (RCC) (Figure 1).

Fig 1
Figure 1. CT scan with contrast of the abdomen and pelvis showed a 3.3-cm abdominal mass within the right posterior kidney, concerning for RCC.

The patient had dysuria related to the recent surgical procedure but reported no hematuria, flank pain, family history of urologic malignancy, or history of smoking. The differential diagnosis included RCC and renal oncocytoma.

The patient subsequently underwent a robotic assisted right partial nephrectomy. Gross examination showed a rubbery, well circumscribed, red-purple, ovoid mass measuring 3.5 × 3.0 × 2.8 cm and confined to the kidney. A thin, intact capsule was noted. The tumor had no variegated or necrotic areas.

Microscopic examination of the mass showed a proliferation of nests, cords, and tubules of oncocytic cells, tightly packed in some areas, and suspended in a hypocellular and loose matrix in other areas. This matrix was most pronounced and scar-like in the central portions of the tumor. The oncocytic cells had a characteristic eosinophilic, granular cytoplasm. The tumor nuclei were central, uniform, and small, with no discernable mitotic activity (Figures 2-4). Based on these findings, a diagnosis of renal oncocytoma was made.


Fig 2
Figure 2. High-power image showing uniform round or polygonal cells that are intensely eosinophilic with granular cytoplasm and with uniform small, round, central nuclei (hematoxylin-eosin, original magnification ×60).


Fig 3
Figure 3. Low-power image showing oncocytoma cells with no perinephric or vascular invasion (hematoxylin-eosin, original magnification ×10).

Fig 4
Figure 4. Low-power image showing an area of central scarring found in oncocytomas (hematoxylin-eosin, original magnification ×10).

Discussion. Renal oncocytomas account for 3% to 7% of all renal tumors.1,2 They occur most often in adults older than 50 years, with peak incidence in the seventh decade of life.3 They occur more commonly in men than in women, with a ratio of 1.2 to 1.4

Although they are benign, renal oncocytomas can coexist with RCC.5,6 They are often difficult to differentiate from RCC because of their similar presentations and similarities in morphologic, histologic, and imaging characteristics.7,8 However, it is important to distinguish between the conditions given the differences in prognosis and treatment. Renal oncocytomas are usually not aggressive and have an excellent prognosis, even among the atypical morphologic types.4 They rarely metastasize to the liver and bones, and surgical intervention is curative when there are no metastasis.4 Renal oncocytomas are often found incidentally on imaging studies, since most patients do not report associated urologic symptoms, but some can present with hematuria, flank pain, and a palpable mass on examination.9,10 Because no precise radiologic criteria exist for distinguishing oncocytomas from a malignant lesion, they cannot be reliably differentiated preoperatively. Our patient underwent partial nephrectomy before the final diagnosis was made. On the other hand, the prognosis of RCC depends on the stage of the disease.11 The earlier stages I and II have a better prognosis than stages III and IV.11 The treatment approach is based on the stage and type of tumor and includes ablation, radiation therapy, chemotherapy, or surgery.

On gross appearance, oncocytomas are usually well circumscribed and resemble normal renal parenchyma with tan or mahogany color on the cut surface, whereas RCC appears golden yellow. Microscopically, oncocytomas have uniform round or polygonal cells that are intensely eosinophilic with granular cytoplasm and with uniform small, round, central nuclei (Figure 2), whereas the histology of RCC depends on its subtype (clear-cell, papillary, or chromophobe RCC). Oncocytomas usually do not have perinephric or vascular invasion (Figure 3), but some authors have reported otherwise in atypical cases.12-14 A central scar is found in oncocytomas but can also be seen in chromophobe RCC (Figure 4).13,15

Sometimes it is difficult to differentiate between RCC and oncocytoma on light microscopy, especially if the tissue sample is small, but studies have shown that immunochemistry staining may help to distinguish these similar masses. Immunochemically, cytokeratin 7 (CK7) is negative to scattered in oncocytoma and negative to focal in clear-cell RCC but is positive in chromophobe and papillary RCC.15 Another marker, CD117, is positive in oncocytoma and chromophobe RCC but negative in clear-cell and papillary RCC.16,17 In a systematic review and meta-analysis, Ng and colleagues18 recommended that a panel of biomarkers—including amylase α1A, Wnt-5a, FXYD2 protein, ankyrin-repeated protein with a proline-rich region (ARPP), CD63, transforming growth factor β1, CK7, S100 calcium-binding protein A1, caveolin-1, and claudin-7—can be useful In differentiating renal oncocytoma from chromophobe RCC. These differentials should be considered before a final diagnosis of renal oncocytoma is made.

Currently, a definitive diagnosis of renal oncocytoma can only be made postoperatively. Further research may be needed to distinguish oncocytoma preoperatively from RCC, since surgical procedures are not without risks.

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