384 Background: Tyrosine kinase inhibitors (TKIs) such as sorafenib are widely used in the treatment of solid tumor malignancies. Incident hypertension with angiogenesis inhibitors has been well-documented in the population of patients with renal cell carcinoma (RCC) where incident hypertension on treatment is associated with improved clinical outcome. Little has been reported about increases in blood pressure with TKIs in other solid tumor malignancies. Methods: We performed a retrospective cohort study examining changes in blood pressure with sorafenib among the 101 patients treated at the University of Pennsylvania on a randomized discontinuation trial examining sorafenib in patients with advanced solid tumor malignancies. Solid tumor diagnoses were established on the basis of tumor histology. Treatment of patients on study with sorafenib was initiated at 400 mg BID. Patients were treated for at least 12 weeks and were evaluated at least every three weeks in the clinic. Blood pressure was recorded at each visit. Sorafenib exposure was recorded by patients in a pill diary. The primary endpoint for this study was a maximal change in blood pressure defined as the difference between baseline blood pressure and highest subsequent recorded systolic and diastolic blood pressures on treatment. Results: 72% of RCC patients developed an increase in systolic blood pressure (SBP) of at least 20 mmHg as compared to 32% of non-RCC patients. The mean increase in SBP on study for RCC patients was 30 mmHg versus 19 mmHg in non-mRCC patients. RCC patients in the top quartile of increased SBP showed a mean increase of 54 mmHg as compared to 35 mmHg for non-mRCC patients. A chi-squared test of proportions and t-tests were used to compare rates and means, respectively. Each of the aforementioned differences were found to be statistically significant with p-values <0.003. These relationships also held true for diastolic blood pressure. There was no difference in SBP between groups in terms of age or sorafenib exposure. Conclusions: In these patients treated with sorafenib the proportion of patients with increased blood pressure and the mean amplitude of change in blood pressure both were significantly greater in the RCC population than in the non-RCC group.