The incidence, predictors, and survival of disappearing small renal masses on active surveillance

Objective: To evaluate the incidence, predictors, and survival for those small renal masses (SRM, solid mass ≤4 cm suspicious for a clinical T1a renal cell carcinoma) that disappear on imaging while undergoing active surveillance (AS). Subjects/patients and methods: The Delayed Intervention and Surveillance for SRM registry prospectively enrolled 739 patients with SRMs. Patients having at least 1 image showing no lesion were considered to have a “disappearing” SRM. Logistic regression assessed predictors of having a disappearing SRM and Kaplan-Meier estimates illustrated relative survival. Results: Of 374 patients enrolled in AS, 22 (5.9%) experienced a disappearing SRM. Mean time to tumor disappearance was 2.0 years (SD = 1.9) and 50.0% reappeared on subsequent CT imaging. SRM disappearance, most commonly encountered on ultrasound imaging surveillance, was independently associated with tumors <1 cm on multivariable analysis (OR = 10.6 (95% CI: 1.1–100.3), P = 0.04). Furthermore, patients with disappearing SRMs were healthier than other patients on AS with no compromise in overall survival during follow-up (5-year survival = 100% vs. 73.2%, P = 0.06). Conclusions: Approximately 5% of SRM on AS will disappear during follow-up on surveillance imaging. Most of these represent artifacts of heterogeneous imaging modalities, including ultrasound, and the SRM will reappear on subsequent imaging. Given the indolent nature of these lesions, disappearance events do not require reflex repeat imaging and patients should continue AS with their original surveillance schedule intact. A smaller percentage of patients undergoing AS for a SRM may have a mass the permanently disappears.