We investigated sequential kidney function for 5 years in 466 patients with clinical stage 1 renal tumors who PN and compared eGFR in each year to the new baseline eGFR which was defined as eGFR at 6 months after surgery. In total cohort, eGFR was significantly decreased year by year ( -5.4% decrease at five year). In addition, the presence of DM, preoperative progressed grade CKD, and high complexity tumor were significant predictive factors for > 15% decline in eGFR from the new baseline to 5-year eGFR by multivariate analysis.
In the present study, eGFR decreased from the new baseline (61.4 ml/min/1.73m2) to 5 year after surgery (57.9 ml/min/1.73m2), meaning an average decrease of 0.70 ml/min/1.73m2 per year. Our study included patients who could completely review renal function in 5 years after surgery, which was rare study as to patients who underwent PN for kidney tumors. On the other hand, natural history of kidney functional decline in general population was previously reported. According to one of the first published study, clearance rate decreased by 1ml/min per year of age between age 40 and 80[12, 13]. According to the Baltimore Longitudinal Study of Aging, creatinine clearance declined by a mean of -0.75 ml/min/1.73m2 per year in a cohort without renal disease, followed up to 23 years, although 35% of individuals in this study did not experience a decline in renal function[13-15] . As for eGFR, the change in eGFR over time was calculated using data on 4380 participants with the mean eGFR baseline 79ml/min/1.73m2 and older adults (65 years) from the Cardiovascular Health Study, which showed that the mean change in eGFR was -0.4 ml/min/1.73m2 per year of follow-up evaluation using the serum creatinin-based equation[13, 16]. Comparing to these previous studies, the results of our study indicating a mean decline in eGFR (0.44 ml/min/1.73m2/year) may be acceptable despite different a study period and different patient backgrounds.
Our study provided that preoperative CKD stage associated with decline in eGFR from the new baseline renal function. Decline in eGFR for five years was 4.2%, 5.5% and 14% in patients with CKD stage 2 or less, CKD stage 3a and CKD stage 3b or more, respectively. Several studies also reported the association between CKD stage and the decline in eGFR. Hemmelgran et al. investigated renal functional change in 10,184 people with 66 years of age or older and demonstrated that progressed CKD stage impacted on the significant decline in eGFR in each category such as sex and DM. For example, the percent decline in mean eGFR was 2.8%, 4.2%, and 15.5% in the subjects with eGFR 60-89, eGFR 30-59 and eGFR < 30, respectively in the cohort of males without DM. Although there were some differences including patient’s background or duration of the study, the trend of renal function deterioration of our data is compatible with the previous study.
DM was a significant factor for renal functional deterioration from the new baseline to 5 years in the present study. In fact, patients with DM had grater decline in eGFR with 10% over the 5-year period, compared to those without DM with 4.5%. According to the study among a community-based cohort of subjects 66 years of age and older, subjects with DM showed the percent decline in eGFR over 2-year period with 6.5% and 7.1% for female and male subjects, respectively. On the other hand, subjects without DM showed the percent decline in eGFR with 2.3% and 3.5% for female and male, respectively. These correlation between subjects with DM and without DM was similar to our study, despite the difference of the study period.
In the present study, patients with a high-complexity tumor had a significant reduction in eGFR from the new baseline over 5 years after surgery compared to those with a low-complexity tumor in multivariate analysis. Although the etiology is uncertain, compensatory hypertrophy in the contralateral kidney might be associated with our result. Park et al. investigated the association between tumor size and contralateral kidney volume before radical nephrectomy, and demonstrated that patients with tumors sized >7 cm had a significantly larger contralateral kidney volume than those with tumors sized 4–7 cm or 4 cm. This indicates that compensatory hypertrophy in the contralateral kidney occurs before surgery in case of large kidney tumors. Additionally, the same group reported that the median contralateral kidney volume change after radical nephrectomy was significantly larger in patients with tumors sized 4 cm or 4–7 cm compared to those with a tumor sized > 7 cm. We can therefore conclude that compensatory hypertrophy in the contralateral kidney in patients with small renal tumors begins right after surgery. Another possible reason may be the decreased ability for compensation. A contralateral kidney with a large tumor is overloaded before surgery compared to that with a small tumor, which results in decreased ability for compensation. In the present study, the tumor size tended to be larger in patients with a high-complexity tumor (40 mm) than in those with an intermediate-complexity tumor (32 mm) and a low-complexity tumor (25 mm). Therefore, less contralateral kidney compensation after surgery might occur in patients with high-complexity tumors than in those with low-complexity tumors, and might associate significantly with decreased eGFR from new baseline until 5 years after surgery. Further examination including volumetric studies of contralateral kidneys is warranted to explain the hypothesis.
The present study has several limitations. First, the study was retrospective, performed in a single institution, and included a population of tertiary care patients. Second, this study included patients who could be completely reviewed renal function for 5 years after surgery; therefore, those who died of any reasons or with missing data were excluded from the study, which suggests that our study did not reflect renal functional change in all patients who underwent kidney tumor surgery. Third, the surgical approach including open, laparoscopic and robot assisted PN was mostly dependent on the study periods, which results in the difference of background. The strengths of this study were the large number of included patients and relatively long-term follow-up renal functional data. In addition, comparison between the new baseline renal function and subsequent postoperative renal function in five years was rare, with regard to patients who underwent PN for renal tumors.
In conclusion, our study showed sequential decline in eGFR from the new baseline for 5 years after surgery for clinical T1 renal tumor. The presence of DM, progressed CKD stage and high complexity tumor associated with decreased change in eGFR from the new baseline to 5-year eGFR. Careful monitoring will be required for patients with such risk to avoid further kidney functional deterioration.