Sorafenib in Treating Patients at Risk of Relapse After Undergoing Surgery to Remove Kidney Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed renal cell carcinoma (RCC) * Clear cell or non-clear cell tumors allowed * Intermediate- or high-risk disease (Leibovich score 3 to 11) * Must have undergone surgery for RCC at least 4 weeks but no more than 3 months prior to study entry * No evidence of residual macroscopic disease on post-operative CT scan after resection of RCC PATIENT CHARACTERISTICS: * WHO performance status 0-1 * WBC \> 3,400/mm³ * Platelet count \> 99,000/mm³ * Creatinine \< 2.5 times upper limit of normal (ULN) * Liver function tests \< 1.5 times ULN * Serum amylase \< 1.5 times ULN * PT/INR \< 1.5 times ULN * PTT \< 1.5 times ULN * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 9 months after completion of study treatment * No cardiovascular conditions, including any of the following: * Cardiac arrhythmias requiring anti-arrhythmic medication * Beta-blockers and digoxin allowed * Symptomatic coronary artery disease or ischemia * Myocardial infarction within the past 6 months * NYHA class II-IV congestive heart failure * No active clinically serious bacterial or fungal infection * No known history of HIV infection * No chronic hepatitis B or C * No other prior malignancy except carcinoma in situ of the cervix or adequately treated basal cell carcinoma * No uncontrolled hypertension PRIOR CONCURRENT THERAPY: * See Disease Characteristics * No prior treatment for RCC other than nephrectomy * More than 30 days since prior and no other concurrent investigational therapy * No concurrent medications that have adverse interactions with sorafenib tosylate including, but not limited to, any of the following: * Rifampin * Grapefruit juice * Ritonavir * Ketoconazole * Itraconazole * Hypericum perforatum (St John's wort) * No concurrent bone marrow transplant or stem cell rescue * No other concurrent drug that targets angiogenesis, especially VEGF or VEGF receptors (e.g., bevacizumab) * No other concurrent drug that targets Ras-pathway or EGFR * No other concurrent anticancer therapy (chemotherapy, immunotherapy, signal transduction inhibition, or hormonal therapy) * Concurrent non-conventional therapies (e.g., herbs or acupuncture) and vitamin or mineral supplements allowed * Concurrent bisphosphonates for prophylaxis of osteoporosis allowed