Abstract: PD59-04
Sources of Funding: None

Introduction

Active surveillance (AS) has become the preferred treatment for small renal masses (SRM) in elderly and the infirm. The vast majority of data comes from small retrospective series with short-term follow-up. We report the natural history of SRM in patients with a five-year median follow-up.

Methods

This prospective cohort included patients undergoing AS for SRMs diagnosed between 2001 and 2011 in Nova Scotia. Age, sex, symptoms at presentation, diameters at diagnosis (cm), tumour location (central, peripheral), degree of endophytic component (1-100%), tumour consistency (solid, cystic), and renal mass biopsy were evaluated. Outcomes observed included progression to treatment or metastatic disease and death, as well as tumor growth rate and its predictors.

Results

The total cohort included 324 patients. Of those, we included 103 patients with 107 SRMs with a diagnosis prior to 2012. Median follow-up time for patients on continued AS was 59.2 months with a median age at diagnosis of 75 years. The median maximum diameter and volume at diagnosis were 2.1 cm (IQR=1.2 cm) and 4.8 cm^3, respectively. 69.9% of population had peripheral masses and 82.5% has solid masses. Biopsies were in 10.7% of patients (36.4% malignant histology). Surgery was performed in 15.5% of patients for tumour growth, gross hematuria, renal vein thrombus, or personal request (68.8% malignant histology). 1.9% of patients developed metastatic disease. In total, 45.6% of the population died from other causes and 1.9% died from kidney cancer. Of the patients on continued AS, 51.5% were alive without metastatic disease and 1.0% were alive with metastatic disease. The average growth rate of all SRMs was 6.2 cm^3/year with an average volume at diagnosis of 9.3 cm^3 (p= 0.0043). Tumor growth rate was significantly different between peripheral and central SRMs (p= 0.0007) with peripheral masses growing at a rate of 1.8 cm^3/year (initial volume at diagnosis= 7.9 cm^3) and central masses growing at a rate of 17.3 cm^3/year (initial volume at diagnosis= 11.4 cm^3). Tumor growth rate of masses that were >3 cm at initial diagnosis was approximately 15 times greater than masses that had an initial diameter of <1 cm (23.5 cm^3/year versus 3.0 cm^3/year; p= 0.0067).

Conclusions

In this cohort with a median follow-up of five years, 45.6% of patients died from other causes and only 1.9% developed metastatic disease. This demonstrates that AS is the preferred treatment for patients who are elderly or infirm. Tumor growth rate can be predicted by initial tumour size and tumor location.

Funding

None