Stage-specific conditional survival in renal cell carcinoma after nephrectomy

Highlights

• Conditional survival after nephrectomy for renal cancer varies by stage of disease.

• There is no conditional survival benefit for stage I and II disease.

• Gains in conditional survival over time are notable in stage III and IV disease.

• Using conditional survival estimates can improve postoperative patient follow-up.

Abstract

Objectives

Conditional survival (CS) represents the probability that a cancer patient will survive some additional number of years, given that the patient has already survived for a certain period of time. CS estimates, therefore, serve as better measures of survival probability compared to standard estimates as they incorporate patient survivorship. Stage-specific CS has not been widely investigated in the context of renal cell carcinoma (RCC) after nephrectomy. We aimed to examine this phenomenon.

Materials and methods

We analyzed retrospective data on a population-based cohort of 87,225 surgically-treated RCC patients extracted from the Surveillance, Epidemiology, and End Results database (2004–2015) and on a similar validation cohort of 1,642 patients from our institution (1995–2015). 5-year cancer-specific CS estimates stratified by stage were obtained using the Kaplan–Meier method. Multivariable Cox regression analyses were performed to evaluate the possible variation in risk of cancer-specific mortality by stage at nephrectomy and with increasing postoperative survivorship.

Results

5-year cancer-specific survival rates at time of nephrectomy for stage I, II, III, and IV patients in the population-based cohort were 97.4%, 89.9%, 77.9%, and 26.7%, respectively. Improvement in 5-year CS was mainly observed in surviving patients with advanced-stage disease; given 1, 2, 3, 4, and 5 years of survivorship after nephrectomy, the subsequent 5-year cancer-specific survival rates were, respectively, 79.3% (+1.8% increase over previous survival probability), 81.3% (+2.5%), 83.3% (+2.5%), 84.3% (+1.2%), and 85.1% (+1.0%) for stage III, and 34.6% (+29.6%), 42.5% (+22.8%), 49.0% (+15.3%), 55.7% (+13.7%), and 58.6% (+5.2%) for stage IV. A similar trend was established in the validation cohort. Findings were confirmed upon multivariable analyses.

Conclusions

CS after nephrectomy for RCC varies dramatically by stage of disease. Gains in CS over time occur primarily among patients with advanced-stage disease. Stage-specific CS estimates can help urologists better plan postoperative surveillance for RCC patients.

Introduction

Survival estimates given at the time of diagnosis or primary nephrectomy for renal cell carcinoma (RCC) provide a static view of risk of mortality and do not reflect how cancer prognosis evolves over time. However, conditional survival (CS), which is derived from the concept of conditional probability [1], [2], measures the probability of future survival for a cancer patient, taking into account any survival time that has already elapsed. As such, CS estimates represent more accurate measures of survival probability with increasing follow-up time. The effect of CS has been previously examined and reported for various malignancies [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], including surgically-treated RCC [17], [18], [19], [20]. Pathologic TNM stage is known to be one of the foremost prognostic factors in patients with RCC [21]. Despite the lack of consensus with respect to the optimal postoperative surveillance protocol for RCC [22], [23], several follow-up protocols, including those recommended by the American Urological Association guidelines [24], the National Comprehensive Cancer Network guidelines [25], and the European Association of Urology guidelines [26], currently use pathologic TNM staging to stratify patient risk. Thus, stratification of CS estimates by pathologic TNM stage can result in more clinically relevant and better individualized prognostic information for RCC patients.

The stage-specific effect of CS in surgically-treated RCC has been previously shown in few studies. One series examined this effect in an institutional cohort of patients, but it was limited by the relatively small sample size [19]. Moreover, progression-free survival was assessed rather than overall or cancer-specific survival, which would have served as more appropriate survival end points. Another series investigated stage-specific CS in RCC after nephrectomy in a population-based cohort from the Surveillance, Epidemiology, and End Results (SEER) Program, using data from 1988 to 2008 [20]. However, SEER only started implementing the Collaborative Stage project, which unified and improved the quality of collected pathologic TNM staging information to meet the American Joint Committee on Cancer (AJCC) criteria, in 2004. The aim of the present study was to evaluate the stage-specific effect of CS in RCC patients treated with nephrectomy, using a contemporary (2004–2015) population-based SEER cohort, and validate the observed effect in a separate institutional cohort of patients. We expected to see a variation in CS benefit by stage of RCC, with greater benefit achieved among patients with advanced disease compared to localized disease.