Robot-assisted Surgical Resection vs. Cryoablation of Localised Renal Cancer - a Randomised Trial of Functional, Oncological and Financial Aspects

The diagnosis and management of renal cell carcinoma (RCC) have changed remarkably rapidly. Although the incidence of RCC has been increasing, survival has improved substantially. As incidental diagnosis of small indolent cancers has become more frequent, active surveillance, robot-assisted nephron-sparing surgical techniques and minimally invasive procedures, such as thermal ablation, have gained popularity. Despite progression in cancer control and survival, locally advanced disease and distant metastases are still diagnosed in a notable proportion of patients.

In 2013, RCC was diagnosed in more than 350.000 people worldwide, making it the seventh most common tumour, and this cancer is associated with more than 140.000 deaths per year. Incidence of RCC varies worldwide, being higher in developed countries than in developing countries. In Europe, mortality from RCC peaked at 4.8 per 100.000 in 1990-94 and had declined to 4.1 per 100.000 (-13%) in 2000-04. In the US, 5-year relative survival rates increased from 50% in 1975-77 to 73% in 2003-09. According to the Danish Cancer Registry, approx. 1000 Danes are annually diagnosed with RCC, of which approx. 25% have a small localised tumour that are potentially eligible for a minimal invasive nephron-sparing treatment modality.

With the expansion of routine imaging for many disorders, patients with RCC are increasingly being identified by chance. Only 30% of patients are diagnosed on the basis of symptoms. Small renal masses (SRM) refers to tumours less than 4 cm I diameter, which have not spread beyond the kidney (T1a tumours). The highest incidence of SRM is seen in patients older than 65 years, who generally present themselves with varying degrees of comorbidity. Thus, minimally invasive treatment modalities are highly relevant in the treatment of RCC in the ever-growing elderly population.

Notwithstanding the advances in the understanding of RCC biology, surgery remains the mainstay of curative treatment. Although radical nephrectomy was the standard of care for the management of renal tumours, the detection of SRMs and accumulating evidence that surgical induced chronic kidney disease can increase patients' morbidity have led to more conservative approaches. Specifically, nephron-sparing surgery, ablative modalities and active surveillance. When treating patients with SRM three competing factors must be considered; comorbidity, renal function and oncological outcome. Active surveillance remains controversial as absolute cut-offs for tumour size and growth rate that should prompt intervention are not well defined. In comparison to radical nephrectomy, nephron-sparing surgery has increasingly been used since observations suggested oncological control similar to radical nephrectomy but with the additional benefit of renal preservation and a reduced risk of cardiovascular events. These functional outcomes become important because patients with organ-confined RCC that has been surgical treated are usually long-term survivors (10-years cancer-specific survival of 85-96%). Today most nephron-sparing surgical procedures consists of robot-assisted partial nephrectomy (RPN).

Although surgery still represents the standard of care for RCC, the use of minimally invasive ablative techniques to treat SRMs has been increasing. Ablative treatment such as cryoablation (CA) were initially contemplated only to patients with a single kidney or those deemed unfit to more extensive surgical procedures. Since an increasing number of reports have shown acceptable oncological control and low complications rates the clinical indications for these procedures has been extending. Most studies of outcomes after CA consist of single-institution retrospective reports with low number of un-randomised patients with short follow-up.