Cancers are getting smaller. Nowhere is this more evident than in the field of renal cancer where the vast majority of tumours are now detected incidentally at imaging for other symptomatology. In fact, this disease in particular illustrates the steady shift towards the detection and treatment of asymptomatic malignancy so as to reduce the cost to healthcare systems and minimise treatment morbidity to patients later in the course of the disease.
The five-year survival rate for renal carcinoma has increased from 34% in 1954 to 62% in 1996 with a 126% increase in the incidence of disease since 1950(1). Whilst a proportion of these tumours will be indolent cancers in elderly patients there has also been a 36.5% rise in the annual mortality attributable to kidney cancer and it therefore remains important to treat this disease, dependent on the clinical circumstances.
Two medical advances have contributed significantly to this improved five-year survival rate. The advent of safe surgical nephrectomy in the 1960's (Robson) and more latterly diagnostic radiology through the incidental detection of early stage disease. In fact imaging has contributed to both the increased incidence and improved survival from renal cancer and there has been an undoubted stage migration of kidney cancer towards T1 (0-7cm), and further, towards T1a disease (0-4cm). Another clear trend has been the urological realisation in recent years that equal oncological outcomes can be achieved through partial and even laparoscopic nephrectomy, so reducing the morbidity of the procedure to the patient; importantly through the preservation of ipsilateral functioning renal parenchyma. These surgical trends and changing tumour presentations now place kidney cancer firmly within the remit of interventional oncology.
Considerable accrued experience and increasingly five-year survival data now demonstrate that T1a renal cancer (0-4cm) can be straightforwardly managed by means of careful image-guided ablation to the benefit of both the patient and health care systems (Figure 1). Large series(2, 3) of 100 or more tumours have confirmed that T1a disease can be ablated at a single session in the vast majority of cases.
Complications have been largely self-limiting or readily treated and have included renal haemorrhage and pelvicalcyeal leaks or strictures. In our own experience (in press with CVIR) of over 120 renal tumour ablations (to end of 2006) treatment was again largely straightforward for sub-4cm disease with a complication rate of 4.2% which included, at worst, a pneumothorax and a duodenal perforation, repaired at open surgery.
In the arena of tumour ablation the manufacturers have worked hard to produce more effective ablation tools and interventional radiologists (IRs) have modified the technique so as to improve treatment outcomes.
Target tumour modulation through 'hydrodissection' (Figure 2) and pre-embolization (Figure 3) have helped to further increase the scope of image-guided ablation for small - to - intermediate volume renal cancers. However it is in the area of accurate image guidance and peri-procedural monitoring that most challenges remain. Cryotherapy involves cell death through repeated freeze-thaw cycles, but perhaps more importantly the evolving, destructive ice-ball is readily apparent at CT and MR monitoring (Figure 4). Renal cancer cells appear to be particularly turgid and susceptible to 'cryoinjury'. Besides RFA there is considerable interest in percutaneous, image-guided cryoablation as a means of renal tumour ablation although there remain significant issues around cost and multiple probe placements.
IR has already made significant contributions to the surgical management of renal cancer through palliative (Figure 5) and pre-operative embolization of larger and caval-invasive tumours. My colleagues - Nigel Hacking and Brian Stedman - pre-embolize vertebral metastases prior to surgical fixation, thereby considerably reducing intra-operative blood loss. Increasingly these lesions are managed by percutaneous ablation and vertebroplasty for palliative purposes.
It has become apparent in recent years that even metastatic renal cancer is, for many patients, part of a more prolonged and not necessarily life-limiting renal cancer diagnosis. More recently the outlook has been further modified by the advent of tyrosine kinase inhibitors, such as sunitinib and sorafenib.
Sorafenib has been shown in a phase 3 randomised study to double median progression - free survival and other agents show considerable promise in influencing tumour anigogenesis and proliferation patterns. For some time it has been suggested that small, indolent renal cancers in older patients do not warrant treatment. Whilst the natural history of these tumours can be prolonged, it is clear that some 15-20% are more aggressive and at present we have no simple technique for identifying this subset of disease. Biomolecular prognostic markers are under development, but until these are available the use of interval imaging remains a very coarse tool for tumour triage. This temporising approach is premised on the morbidity of more traditional resective techniques and importantly the cure must not be worse than the disease. The advent of minimally invasive IR techniques such as careful image-guided ablation favours the treatment of small volume disease at presentation and should contribute further to the reduced mortality from renal cancer in years to come.
References
1: Pantuck AJ, Zilman A, Belldegrun AS. The changing natural history of renal cell carcinoma. J Urol. (2001) 166: 1611-1615
2. Gervais DA, McGovern FJ, Arellano RS, McDougall WS, Mueller PR. Radiofrequency ablation of renal cell carcinoma: indications, results and patient management over a 6-year period of 100 tumours. AJR (2005) 65 : 877-881.
3. Zagoria RJ, Traver MA, Werle DM, Perini M, Hayasaka S, Clark PE. Oncologic efficacy of CT-guided percutaneous radiofrequency of renal cell carcinoma. AJR (2007) 189: 429-436.
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