Small renal masses progressing to metastases under active surveillance: a systematic review and pooled analysis

Background: The authors systematically reviewed the literature and conducted a pooled analysis of studies on small renal masses who underwent active surveillance to identify the risk progression and the characteristics associated with metastases.

Methods: A search of the MEDLINE database was performed to identify all clinical series that reported the surveillance of localized renal masses. For studies that reported individual-level data, clinical and radiographic characteristics of tumors without progression were compared with the characteristics of tumors that progressed to metastases.

Results: Eighteen series (880 patients, 936 masses) met screening criteria; and, among these, 18 patients were identified who had tumors that progressed to metastasis (mean, 40.2 months). Six studies (259 patients, 284 masses) provided individual-level data for pooled analysis. At a mean (± standard deviation) follow-up of 33.5 ± 22.6 months, the mean initial greatest tumor dimension was 2.3 ± 1.3 cm, and mean linear growth rate was 0.31 ± 0.38 cm per year. Sixty-five masses (23%) exhibited zero net growth under surveillance, and none of those masses progressed to metastasis. A pooled analysis revealed increased age (age 75.1 ± 9.1 years vs 66.6 ± 12.3 years; P = .03), an initial greatest tumor dimension (4.1 ± 2.1 cm vs 2.3 ± 1.3 cm; P < .0001), initial estimated tumor volume (66.3 ± 100.0 cm(3) vs 15.1 ± 60.3 cm(3) ; p = .0001), linear growth rate of (0.8 ± 0.65 cm per year vs 0.3 ± 0.4 cm per year; P = .0001), and a volumetric growth rate of 27.1 ± 24.9 cm(3) per year (vs 6.2 ± 27.5 cm(3) per year; P < .0001) in the progression cohort.

Conclusions: A substantial proportion of small renal masses remained radiographically static after an initial period of active surveillance. Progression to metastases occurred in a small percentage of patients and generally was a late event. The current results indicated that, in patients who have competing health risks, radiographic surveillance may be an acceptable initial approach, and delayed intervention may be reserved for patients who have tumors that exhibit significant linear or volumetric growth.