56: ACTIVE SURVEILLANCE VERSUS MICROWAVE ABLATION: COMPARING RENAL AND ONCOLOGIC OUTCOMES FOR cT1a SMALL RENAL MASSES

Background: Minimally invasive treatments which preserve renal function are gaining favor in the management of small renal masses (SRM) due to comparable survival outcomes with greater treatment potential in more comorbid patients. We evaluated oncologic and renal function (RF) outcomes between two of these treatments: active surveillance (AS) and microwave ablation (MWA).

Methods: Prospective data on patients with cT1a (≤4 cm) SRMs treated with AS or MWA were collected from our single-institution database from 2015. RF was measured before management, at 6-, and at 12-months of following. Differences were evaluated using Chi-squared and Student’s t-test.

Results: A cohort of 111 AS and 112 MWA patients were eligible. Tumor diameters were 2.2 versus 2.8 cm (p < 0.001) for AS and MWA, respectively. For AS, masses grew 1.2 (IQR 0-3.8) mm/year with sixteen (14.4%) progressing to treatment after 21.3 months (8.8-39.1). Eleven progressed for growth concerns (≥3 cm or ≥5 mm/year), 3 for patient preference, 1 for liver-transplant eligibility, and 1 unspecified. For MWA patients, 5 (4.5%) had recurrences after 22.3 (13.0-24.9) months. There was no difference in metastasis between treatment modalities. There was 1 cancer-related death in MWA cohort. Surgical complications were significantly higher (p=0.002) in MWA (15%) versus AS patients who later required treatment (2.7%). Changes in RF measured by CKD stage progression and 30% eGFR decline at 6 months and 1 year were not different between cohorts. RF was worse at 6 months for MWA patients but improved by 1 year.

Conclusions: Active surveillance for RCC has been shown to be effective for selected SRM patients. MWA is emerging as a safe and effective treatment of SRM. While both modalities have no difference in CKD progression, metastasis, or overall death, patients on AS with tumors < 3 cm are at lower risk for procedural complications than MWA.