561 - RCC Tumor Morphology and Recurrence in Tumors Greater Than 3.1 Cm

Purpose: Improving performance of cryoablation for larger Renal Cell Carcinoma (RCC) tumors is an area of active research {1,2,3}. However, the relationship between tumor features, particularly for tumors larger than 4 cm, and recurrence is not fully understood {1,4,5}. The goal of this study was to explore the relationship between exophytic tumor morphology and recurrence in larger tumors.

Materials and Methods: This study was conducted under an IRB approved by our institution. All patients who underwent cryoablation from 1/1/2015 - 1/30/2021 for tumors greater than 3.1 cm in maximum diameter were identified using an internal search engine (n = 39). Patients were excluded based on a lack of curative intent (n=4), no imaging or follow up data (n=7), or aborted procedure due to intra-operative complication (n=1). Predominantly exophytic (greater than 50 %) tumors were identified by radiology report if available or by image interpretation. For tumors greater than 4 cm (n=11), exophytic volume and total volume were estimated by manual segmentation. Recurrence was the primary end point and was defined as any definitive evidence of recurrence per the reporting radiologist. Fisher’s exact test was used for categorical analysis of ablations and Student’s t-test was used for volumetric analysis.

Results: Out of a total of 27 tumors, 17 were predominantly exophytic. The median time to follow up was 43 months (IQR: 27.5 - 57.0). There were n=8 instances of recurrence (33.3%), of which 2 (7.4%) were in predominantly exophytic tumors and 5 (18.5%) were in tumors greater than 4 cm. For all tumors, there was a higher rate of recurrence in non-exophytic morphology (60.0% vs 11.8%, p = 0.025) with a relative risk of 5.1 (95% CI: 1.3 - 20.6). When comparing tumors greater than 4 cm with and without recurrence, there was no significant difference in mean tumor volume (45 mL vs 37 mL, p = 0.44) however, tumors with recurrence had a lower component of exophytic volume (9 mL vs 27 mL, p =0.03). The only recurrence in a predominantly exophytic tumor larger than 4 cm occurred 8 years after ablation.

Conclusion: Non-exophytic morphology had a higher risk of recurrence in RCC greater than 3.1 cm with this effect predominantly driven by tumors greater than 4 cm. For tumors greater than 4 cm, recurrence was associated with lower exophytic volume however, the overall volume was similar in tumors with and without recurrence. Larger sample sizes are needed, and further research is warranted to determine if this difference is due to technical challenges with ablation, patient characteristics, or underlying tumor biology.