The effects of sorafenib and sunitinib on bone turnover markers in patients with bone metastases from renal cell carcinoma
e16145 Background: Bone metastases (BM) from renal cell carcinoma (RCC) are common and associated with poor outcomes. While the multi-tyrosine kinase inhibitors (TKI's) sunitinib and sorafenib have advanced the treatment of metastatic RCC, their efficacy on BM is unknown. Urinary N-telopeptide (uNTX) is a marker of bone turnover measured in nmol/mmol creatinine. Elevated uNTX levels correlate with an increased risk of skeletal related events and mortality in patients receiving bisphosphonates for BM from a range of primaries. In this pilot biomarker study we sought to prospectively evaluate the effects on BM of these multi-TKI's in RCC patients. Methods: Eligible patients had advanced RCC, at least one BM evident on imaging and no bisphosphonate exposure within 4 weeks. UNTX levels (OsteoMark) were measured at; baseline and weeks-1, 4, 8 and 12 after commencing either sunitinib or sorafenib. The primary endpoint was the percentage change (Ch) in uNTX levels from baseline. Serum samples were also collected for KIT and VEGFR-2 (Quantikine). Patients also completed pain (including bone pain) and quality of life questionnaires. Results: The uNTX results on the first 9 patients are presented in the table below (7 received sunitinib and 2 sorafenib). In this group, sVEGFR-2 and sKIT levels fell by week-1 and 4 respectively and at week-12 the mean % changes (95% CI) were -34% (-0.53,-0.14) and -38% (-0.58,-0.18). Conclusions: In patients with BM from RCC and at least moderately elevated uNTX levels at baseline, these multi-TKI's show a significant trend to decrease uNTX levels, but perhaps not as effectively as bone-specific therapies (e.g. bisphosphonates) do in other malignancies. SVEGFR-2 and sKIT levels also fell across the patient group over the same period. This pilot data raises questions about the activity of the multi-TKI's in BM from RCC and further research is needed. [Table: see text] [Table: see text]