What is oncocytoma (renal oncocytoma)?

From the Guidelines

Oncocytoma is a benign kidney tumor that should be managed with surgical removal, preferably partial nephrectomy, to minimize morbidity and mortality, while also preserving kidney function and quality of life. The diagnosis of oncocytoma can be challenging, as it requires distinguishing it from renal cell carcinoma, which can be difficult through imaging alone 1. According to the most recent study published in 2021, oncocytoma is characterized by a distinctive gross appearance, architectural growth patterns, cytoplasmic, and nuclear characteristics, and strict adherence to these features allows for accurate diagnosis in the majority of cases 1.

Some key characteristics of oncocytoma include:

• A well-circumscribed, mahogany-brown mass
• Large cells with abundant granular cytoplasm called oncocytes
• Absence of coagulative necrosis, well-formed papillary formations, and brisk or atypical mitotic activity
• Immunohistochemical labeling for CK7 is usually restricted to rare, scattered cells, typically accompanied by diffuse reactivity for KIT (CD117), and negative reactivity for vimentin

The management of oncocytoma typically involves surgical removal, though active surveillance may be appropriate for smaller tumors in elderly patients or those with significant comorbidities 1. The prognosis is excellent, as oncocytomas do not metastasize and rarely recur after complete removal 1. Regular follow-up imaging is recommended to ensure there is no recurrence.

It's worth noting that the European Association of Urology guidelines on renal cell carcinoma recommend the use of computed tomography (CT), ultrasound (US), and magnetic resonance imaging (MRI) to detect and characterize renal masses, but these imaging modalities cannot reliably distinguish oncocytoma from malignant renal neoplasms 1. Therefore, a detailed, multidisciplinary assessment of a patient’s overall medical condition and functional status is crucial in determining the best course of management for oncocytoma.

In terms of quality of life, surgical removal of oncocytoma can help alleviate symptoms such as flank pain, hematuria, or a palpable mass, and can also provide peace of mind for patients who are concerned about the potential risks of leaving a tumor in place. However, active surveillance may be a viable option for some patients, particularly those with small tumors or significant comorbidities, and can help minimize the risks associated with surgery. Ultimately, the decision to pursue surgical removal or active surveillance should be made on a case-by-case basis, taking into account the individual patient's unique circumstances and priorities.

From the Research

Definition and Diagnosis of Oncocytoma

• Oncocytomas are benign tumors often diagnosed incidentally on imaging 2
• Biopsy material may be insufficient to exclude a diagnosis of chromophobe renal cell carcinoma 2
• Renal oncocytoma is a benign tumor of the kidney, typically treated surgically or via ablation therapy 3

Treatment and Management of Oncocytoma

• Active surveillance is a suitable option for patients with biopsy-proven oncocytoma 2, 4, 5
• Stereotactic body radiation therapy (SBRT) can be considered for patients who decline surgery or ablation therapy, or when the pathologic diagnosis of the lesion is in doubt 3
• Patients opting for active surveillance should be made aware that a diagnosis of oncocytoma following biopsy is associated with some degree of uncertainty due to the difficulty of differentiating them from other oncocytic renal neoplasms 2

Growth Rates and Outcomes of Oncocytoma

• The annual growth rate of oncocytoma was 0.14 cm, compared to 0.38 cm for chromophobe renal cell carcinoma 2
• The majority of oncocytomas (74%) and chromophobe renal cell carcinomas (67%) followed up to the 3-year mark had grown 2
• Mean tumor growth was 0.24 cm/year in patients with biopsy-proven renal oncocytomas on active surveillance 4
• No predictive factors of tumor growth could be identified, but the tumor growth rate was low, and biopsy efficacy was high 4

Correlation between Biopsy and Surgical Specimen

• The correlation between biopsy and surgical specimen was 92% 4
• Discrepancy between renal mass biopsy and final histology was 32.0% in surgically treated tumors, with 24 presenting malignant tumors 6
• The only predictive factor of a discrepancy between biopsy and definitive histology was a biopsy done outside of the center 6