BACKGROUND There are various alternative first-line therapeutic options besides tyrosine kinase inhibitors (TKIs) for metastatic renal cell carcinoma (mRCC). To inform therapeutic decision-making for such patients, this study aimed to identify predictive factors for resistance to TKI. METHODS A total of 239 cases of mRCC patients who received first-line TKI therapy were retrospectively studied. Patients with a radiologic diagnosis of progressive disease within 3 months after initiating therapy were classified as primary refractory cases; the others were classified as non-primary refractory cases. The association between primary refractory cases and age, gender, pathology findings, serum c-reactive protein (CRP) level, metastatic organ status, and 6 parameters defined by the International Metastatic Renal Cell Carcinoma Database Consortium were analyzed. RESULTS Of 239 cases, 32 (13.3%) received a radiologic diagnosis of progressive disease within 3 months after initiating therapy. The rates of sarcomatoid differentiation, hypercalcemia, a serum CRP level of 0.3 mg/dL or higher, presence of liver metastasis, anemia, and time from diagnosis to treatment interval of less than a year were significantly higher in the primary refractory group. Multivariate analysis showed that sarcomatoid differentiation, hypercalcemia, a serum CRP level of 0.3 mg/dL or higher, and liver metastasis were independently associated with primary refractory disease. A risk-stratified model based upon the number of patients with these factors indicated rates of primary refractory disease of 4.0%, 10.1%, and 45.0% for patients with 0, 1, and 2 or more factors, respectively. CONCLUSIONS Sarcomatoid differentiation, hypercalcemia, an elevated serum CRP level, and presence of liver metastasis were associated with primary refractory disease in mRCC patients receiving first-line TKI therapy. These results provide clinicians with useful information when selecting a first-line therapeutic option for mRCC patients.