2.1. Data Source and Patient Selection

All data in this study was obtained from the Surveillance, Epidemiology, and End Results (SEER) database (available at https://seer.cancer.gov/). The data of incidence and survival of RCC patients were collected from nine original SEER sites. Cases diagnosed with RCC between 1977 and 2016 were enrolled, which were selected by the variables of: primary site code: C64.9—Kidney, NOS; ICD-O-3 histologic codes: 8310 and 8312 for Clear Cell, 8260 for papillary and 8317 for chromophobe [7, 8]; sex (male and female); race (blacks, whites, and Others: American Indian/AK Native, Asian/Pacific Islander); Age at diagnosis (0–29, 30–39, 40–49, 50–59 and 60+); and SES (low poverty, medium poverty, and high poverty). Area SES was determined by the county poverty rate [9] which was defined as follows: areas with low poverty (less than 10% of the population below the poverty level); areas with medium poverty (10 to 19.99% of the population below the poverty level); and areas with high poverty (20% or more of the population below the poverty level). Considering that patients in high poverty group were few, we integrated the medium– and high-poverty into one group. All cases in this study were primary and the first diagnosed with RCC. Cases diagnosed by autopsy and died from RCC reported in death certificates were not included.