Renal oncocytoma: landscape of diagnosis and management

Abstract

Renal oncocytoma represents between 6% and 12% of T1 renal tumours in surgical series [1, 2]. Contemporary imaging cannot differentiate oncocytoma from malignant renal cell carcinoma (RCC). Uptake of renal tumour biopsy in clinical practice has been variable [3] and surgery with partial or radical nephrectomy is the first line in the management of RCC [4,5]. Many patients with renal masses therefore undergo empirical surgery for presumed RCC but have a postoperative histological diagnosis of benign oncocytoma. While nephron-sparing and minimally invasive surgical techniques have undoubtedly improved surgical outcomes and reduced morbidity, there remains substantial risk associated with surgical resection. Recent national data for the surgical management of oncocytoma showed that 20% of patients experienced inpatient complications, and there was a 60-day mortality rate of 0.4% [6]. To understand the landscape of current oncocytoma diagnosis and management, we conducted a clinician survey to establish clinical practice. Sixty-eight clinicians from six countries took part in an online questionnaire openly distributed via social media. Just over half of respondents were UK-based, one-third were from North America, and the remainder were from across Europe, Africa and Australasia. The majority of respondents were consultants (72%), and more than half (54%) were involved in over 40 radical or partial nephrectomy cases per year. The majority (54%) saw six or more patients a year with renal oncocytoma in their practice. Renal tumour biopsy of small renal masses (≤4 cm) was routine practice for only 29% of respondents, 20% offered it ‘often (20–50% of the time)’, 26% ‘occasionally (10–20% of the time)', and 25% offered it ‘rarely’ or ‘almost never (<10% of the time)’. Barriers to biopsy were identified as high non-diagnostic rate, concern regarding hybrid tumours, diagnostic accuracy and it not being standard practice in the department. Each survey participant was invited to describe their usual initial management strategy for biopsy-confirmed oncocytoma in a variety of clinical scenarios. Clinical scenarios involved patients of different ages (50, 60 and 80 years), American Society of Anaesthesiologists scores (1–2 or 3–4) and tumour sizes (3 cm or 6 cm). A chi-squared test was used to assess if the proportion of clinicians who would usually adopt initial conservative management with active surveillance or watchful waiting was associated with patient or tumour characteristics. The results for patients aged 60 years are shown in Fig. 1. An initial conservative management strategy with active surveillance or watchful waiting was associated with smaller tumours (P < 0.001), and older (P < 0.001) and more comorbid patients (P < 0.001), with the majority of respondents usually adopting a conservative strategy for small tumours in elderly or comorbid patients. However, there was a lack of consensus for the management of younger patients and larger tumours. For example, a 3-cm oncocytoma diagnosed in a fit 50-year-old patient would usually be managed with active surveillance or watchful waiting by 52% of respondents, and surgery or ablation by 33%, while the remaining 15% would usually adopt either strategy according to patient preference. Similarly, for a fit 60-year-old patient with a 6-cm oncocytoma, 47% would usually treat with surgery or ablation, and 44% with active surveillance, with 9% adopting either strategy according to patient preference. There was also variation in preferred imaging method for surveillance of biopsy-confirmed oncocytoma, with 49% favouring CT, 36% ultrasonography and 15% MRI. For frequency of surveillance imaging, two-thirds of respondents favoured imaging at 6 months and annually thereafter across each imaging method. The majority of respondents agreed that a change in imaging characteristics (87%), development of symptoms (61%) and an increase in size >25% in 1 year (61%) would warrant a change in management strategy. The survey also demonstrated variation in follow-up regimens for patients with completely surgically excised oncocytoma. After complete surgical resection of an oncocytoma with no aggressive features on histology, 54% would discharge the patient after the first postoperative review, while 22% would continue surveillance imaging for up to 5 years. If surgical pathology demonstrated either fat or vascular invasion, however, only 14% chose to discharge after the first postoperative review, with 49% favouring surveillance imaging for up to 5 years. Strengths of the present study include the snapshot of international practice from a large number of high-volume surgeons. Limitations include the fact that the survey was not distributed to all practising urologists, and there may be bias introduced by recruiting clinicians via social media networks. Additionally, patient factors but not surgeon factors influencing diagnostics and management strategy were evaluated. The poor uptake of renal tumour biopsy highlights the need for improved diagnostics of benign renal tumours that are accurate and acceptable to patients and clinicians alike. Technetium (99mTc)-sestamibi single-photon emission CT (SPECT)/CT has shown promise in small trials in the USA and Sweden in distinguishing benign oncocytoma from RCC [7-9]. 99mTc-sestamibi is a radiotracer preferentially taken up by cells with abundant mitochondria such as oncocytoma, and actively transported out of cells in RCCs. Oncocytomas therefore light up brightly on SPECT/CT, appearing ‘hot’, while RCCs are devoid of tracer and appear ‘cold’. A prospective study of 50 patients reported sensitivity and specificity of 87.5% and 95.2%, respectively, for 99mTc-Sestamibi SPECT/CT in diagnosing oncocytomas and indolent hybrid oncocytic/chromophobe tumours [7]. In our clinician survey a majority of respondents expressed interest in recruiting patients to a trial assessing the utility of 99mTc-Sestamibi SPECT/CT in the evaluation of renal masses, with 76% responding ‘yes’ and 21% responding ‘potentially – need more information’. A prospective single-centre trial has recently opened in the UK to assess the acceptability and feasibility in the NHS setting (ISRCTN23705289). The survey demonstrates that the majority of participating clinicians support management of renal oncocytomas with surveillance in select clinical scenarios; however, it also demonstrated variable practice, which highlights research gaps in the field. Key evidence gaps highlighted by this survey are underpinned by the lack of understanding of the natural history of oncocytomas and the dearth of randomized controlled trials to inform best practice. Our own group has reported the safety of oncocytoma active surveillance in just under 100 patients over a median follow-up of 2 years [10], consistent with smaller longitudinal cohort studies [11, 12]. However, reporting of outcomes over the longer term is needed to increase confidence in managing these tumours conservatively in patients with long life expectancy. Research into tumour behaviour stratified by size at presentation may also help select patients for surveillance. Further, tumour recurrence rates for surgically excised oncocytoma both with and without invasive features on pathology are required to inform appropriate surveillance strategies after operative management. Finally, well-designed randomized controlled trials are required to provide high-level evidence for guideline recommendations and to standardize practice for each stage of the patient pathway (diagnosis, management and follow-up). We would like to thank all of the clinicians who kindly participated and shared the survey with their networks. None declared.

Topics & Concepts