BERKELEY, CA (UroToday.com) - The incidence of small renal mass (SRM) has been rising, owing to the increased use of imaging for various purposes. SRM is a CT- or MRI-detected, contrast-enhanced solid tumour less than 4 cm. According to contemporary literature, up to 20% of SRMs are benign, 60% are indolent renal cell carcinomas (RCC), and 20% are aggressive tumours. The management of SRM has created both a diagnostic and therapeutic dilemma for urologists around the world. Although renal tumour sampling has been advocated for its high accuracy, there is an increasing demand for non-invasive methods to differentiate benign from malignant lesions and to predict the chance of progression based on tumour subtypes.
We studied the metabolic characteristics of angiomyolipoma (AML) and RCC subtypes with 18F-FDG and 11C-acetate PET/CT. This is the first study to show that 11C-acetate PET/CT helps in differentiating “fat-poor AML” from RCC. It also shows that dual-tracer PET/CT has value in diagnosis of RCC subtypes and predicting survival.
AML is the most common benign renal tumour, often characterized by the presence of macroscopic fat content on CT scan. However, the fat content can be less than 25% in 50% of AML. An uncommon variant is the minimal fat AML, which accounts for 5% of renal AML and can be difficult to be differentiated from RCC on traditional CT scan. Previous attempts to distinguish the above two entities include CT histogram analysis, chemical-shift MRI, and attenuation measurement histogram analysis. The results have been disappointing so far. The present study is the first reported use of dual-tracer PET/CT in renal AML. All AML showed negative
The present study is also the first to describe the use of dual-tracer PET/CT in various RCC subtypes with cancer detection sensitivity of 90%. All chromophobe and type I papillary RCC, the more indolent RCC subtypes, were avid only for 111C-acetate but not 11F-FDG. Type II papillary and collecting duct RCC, the more aggressive tumours, were avid for 18F-FDG only. Clear cell RCC had variable dual-tracer uptake. Low-grade clear cell RCC was more likely detected by 11C-acetate than 18F-FDG. The FDG SUV max ratio was significantly greater in high than low-grade clear cell RCC. Primary RCC with FDG avidity was found to be an independent predictor of RCC recurrence in 3 years’ time.
With advances in understanding of renal tumour biology and cardiovascular morbidities of chronic kidney disease, the paradigm of SRM surgical treatment has changed dramatically over the last two decades. It ranges from active surveillance for benign disease, to thermal ablation for indolent tumours and nephron-sparing surgery for aggressive T1 RCC. Dual-tracer PET/CT may contribute to the armamentarium of diagnostic and prognostic tools in SRM management. Prospective large-scale studies may further clarify the role of dual-tracer PET/CT in predicting RCC progression and standardize the cut-off values of indolent versus aggressive tumours. Hopefully our patients in future will not only depend on the growth rate of renal tumours to decide on the most appropriate management.
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Kwan-Lun Ho, MBBS,a Kossen Man Tzit Ho, MD, PhD,b and Chi-lai Ho, MDc as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
a Division of Urology, Department of Surgery, The University of Hong Kong, China
b Hong Kong Urology Clinic, Hong Kong, China
c Department of Nuclear Medicine & PET, Hong Kong Sanatorium & Hospital, Hong Kong, China