Active Surveillance for Small Renal Masses:
Lessons Learned over the Past Decade
with a Focus on the DISSRM Registry
Introduction
Small renal masses (SRM), defined as solid cortical neoplasms
of the kidney less than 4 cm, comprise approximately
40% of all newly diagnosed renal tumors and are
most-often detected incidentally when working up another
medical complaint.1-4 The discovery of a SRM presents
a substantial challenge to patients and their health-
care providers. Given the biological heterogeneity of
SRMs, it is often difficult to determine preoperatively
whether a SRM is a benign lesion, an indolent malignant
tumor, or, most worrisome, an aggressive malignancy
(Figure). Consequently, a significant number of patients
with small benign masses undergo unnecessary nephrectomy
in the US yearly.5
Active surveillance (AS) with rigorous clinical followup
and scheduled serial imaging has emerged over the
past decade as a safe management strategy in patients
with SRMs and particularly those with indolent or lowgrade
disease. Recent evidence, however, shows that the
adoption of AS for SRMs has been outpaced by robotic
surgical extirpation and that the diffusion of robotic technology
is propagating overtreatment of SRMs.6 To minimize
this, better patient selection criteria for guiding the
decision to undergo AS versus primary intervention need
to be defined, and AS protocols should be optimized. In
this review, we will discuss the lessons learned over the
past years in AS with particular focus on our experience
with the Delayed Intervention and Surveillance for Small
Renal Masses (DISSRM) registry.
Rethinking Growth Rates and Progression
Establishing optimal criteria for patient selection for AS
and identifying proper triggers for delayed intervention
remain a challenge in the management of SRMs. While
108 Kidney Cancer Journal
SRMs generally grow slowly, linear growth rate, which is
the change in maximum tumor diameter over time and
usually expressed in cm/year, is believed to be an objective
parameter for guiding patient treatment and currently
serves as the most commonly used metric for
recommending intervention in patients managed by AS.7
An up-to-date and robust systematic review showed
that linear tumor growth rate varied dramatically among
published series on AS for localized renal masses.8 The authors
reported a median linear growth rate of 0.37
cm/year (IQR 0.15-0.7) for clinically localized renal
masses (cT1-2); in patients with cT1a masses (SRMs), median
growth rate was 0.22 cm/year (IQR 0.11-0.27), and
in those with cT1b-2 masses, it was 0.45 cm/year (0.34
and 0.57 in 2 series). Recent prospective data from the
Fox Chase Cancer Center (FCCC) indicate a median
growth rate of 0.19 cm/year for localized renal masses.9
In two major prospective experiences with AS specifically
for SRMs, the DISSRM registry10 and the Renal Cell Carcinoma
Consortium of Canada (RCCC)11, median linear
tumor growth rates appear to be similarly low at 0.09 and
0.12 cm/year, respectively.12,13 It is important to note,
however, that a significant proportion of SRM patients
on AS have zero or negative growth rates. In fact, contemporary
data on growth rate outcomes suggest that
most SRMs demonstrate non-linear growth over time,
with alternating periods of positive, zero, and negative
growth.12 Mir, et al. reported that zero tumor growth
ranged from 10% to 44% in currently published series.8
An updated DISSRM analysis of growth kinetics revealed
that 41% of masses (n = 114) had a zero or negative
growth rate.12 Similarly, 33% and 36% of SRMs in the
RCCC and the FCCC experiences were found to have zero
or negative growth.9,13
Progression in the prospective DISSRM registry is defined
as any of the following: (1) linear growth rate >0.5
cm/year, (2) greatest tumor diameter >4.0 cm, (3) evidence
of metastatic disease, or (4) elective crossover (due
to change in patient preference or improvement in patient
health status)10; all these currently represent indications
for delayed intervention in SRM patients
managed by AS.
Joseph G. Cheaib, MD, MPH
Post-Doctoral Research Fellow
Department of Urology,
The James Buchanan Brady
Urological Institute
Johns Hopkins University
School of Medicine
Baltimore, Maryland
Phillip M. Pierorazio, MD
Associate Professor of Urology
and Oncology
Department of Urology,
The James Buchanan Brady
Urological Institute
Johns Hopkins University
School of Medicine
Baltimore, Maryland
Keywords: small renal masses (SRM), benign lesion, malignant tumor,
DISSRM registry, active surveillance, renal mass biopsy, growth rate,
pulmonary imaging.
Corresponding Author: Joseph Cheaib, MD, MPH, Post-Doctoral Research
Fellow, The James Buchanan Brady Urological Institute, Johns Hopkins
University School of Medicine, 600 N. Wolfe Street, Park 200E, Baltimore,
MD 21287; P: 410-972-8080 | Email:jcheaib1@jhu.edu