Population-based assessment of cancer-specific mortality after local tumour ablation or observation for kidney cancer: a competing risks analysis

Objectives: To examine, using competing risks regression, differences in cancer-specific mortality (CSM) that might distinguish between local tumour ablation (LTA) and observation (OBS) for patients with kidney cancer. Patients and Methods: The study focused on 1 860 patients with cT1a kidney cancer treated with either LTA or OBS between 2000 and 2009 in the Surveillance Epidemiology and End Results-Medicare database. Propensity-score matching was used. The study outcome was CSM. Multivariable competing risks regression analyses, adjusting for other-cause mortality as well as patient (including comorbidities) and tumour characteristics, were fitted. Results: Overall, fewer patients underwent LTA than OBS (30 vs 70%; n = 553 vs n = 1 307). Compared with patients in the OBS group, those in the LTA group were younger (median age 77 vs 78 years; P < 0.001), more likely to be white (84 vs 78%; P = 0.005), more frequently married (59 vs 52%; P = 0.02) and more frequently of high socio-economic status (54 vs 45%; P = 0.001). After propensity-score matching, 553 patients who underwent LTA and 553 who underwent OBS remained for subsequent analyses. The mean standardized differences of patient characteristics between the two groups were <10%, indicating a high degree of similarity. After LTA or OBS, the 5-year CSM estimates from Poisson regression-derived smoothed plots were 3.5 and 9.1%, respectively. In multivariable competing risks regression analyses, LTA use was found to have a protective effect on CSM (hazard ratio 0.47 [95% confidence interval 0.25–0.89]; P = 0.02). Conclusions: After adjustment for comorbidity and tumour characteristics in elderly patients with kidney cancer, LTA was associated with a clinically and statistically significant protective effect on CSM, compared with OBS. This advantage of LTA deserves consideration when obtaining informed consent.