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MP14-01 NATURAL HISTORY OF RENAL ANGIOMYOLIPOMA (AML) FAVORS SURVEILLANCE AS AN INITIAL APPROACH

INTRODUCTION AND OBJECTIVES: Traditionally, renal angiomyolipoma (AML) >4cm were treated with (angioembolisation, radiofrequency ablation, surgery) due to the risk of hemorrhage. The aim of the study was to delineate the natural history of AMLs including growth rates and need for intervention. METHODS: A retrospective review and update was performed of a previously reported AML series from a radiology database that identified all renal AML lesions between 2002 and 2013 at the Princess Margaret Cancer Center which have now been followed until 2018. We defined lesion size by maximum axial diameter and lesion size at baseline was categorized as ⩽4 or >4 cm. The primary end point was the growth rate of untreated AMLs. We used a linear mixed-effects model to evaluate the association among growth rate, size, and patient factors as well as interventions. RESULTS: A total of 458 patients with 593 AMLs were identified during the study period with a median follow up of 64.8 months. 90% of the lesions were <4cm at diagnosis. 33 (5.6%) AMLs required 35 interventions- 27 embolizations, 2 RFA, 5 had surgery and 1 was treated with mTOR inhibitors. The indications for intervention included 25 for growth, 5 due to a bleed, 3 for patient anxiety and 2 for pain. The median size at intervention was 5.1cm. The average number of scans per lesion (prior to treatment) was 4.5 (range of 1 to 23). For lesions with >1 scan, the median frequency of scans was 0.87 per year. Most (94%) of lesions grew slowly (growth rate of 0.25 cm per year) during the period of observation. The linear mixed-effects model showed that the growth rate (slope) of log-transformed maximal axial diameter was not significantly different between lesions ⩽ 4 cm (0.02 log cm per year) and those > 4 cm (0.01 log cm per year) (p = 0.23). CONCLUSIONS: This large single institution updated series on renal AMLs demonstrates early intervention is not required regardless of the traditional 4cm cut off. The vast majority of AMLs are indolent lesions that are predominantly asymptomatic. Follow up should be no more frequent than annually. Source of Funding: None