Assessment of response to anti-angiogenic targeted therapy in pulmonary metastatic renal cell carcinoma: R2* value as a predictive biomarker

To evaluate the utility of MR R2*-mapping and the optimal time-point for assessing the response of pulmonary metastatic renal cell carcinoma (mRCC) to anti-angiogenic targeted therapy (aATT). The exploration-sample group and the validation-sample group consisted of 22 and 16 patients. The parameters of MR R2*-mapping, including the R2* value at each time-point (R2*_base, R2*_1cyc and R2*_2cyc) and change between different time-points (R2*_{(1cyc-base)/base}, R2*_{(2cyc-base)/base} and R2*_{(2cyc-1cyc)/1cyc}), were evaluated with a receiver-operating-characteristic analysis, and a cut-off value derived from the clinical outcome was applied to the Kaplan-Meier method to assess the value of R2* mapping and Response-Evaluation-Criteria in Solid Tumours (RECIST) during treatment evaluation. The inter-, intra-observer agreements and inter-scan consistency were excellent (p > 0.80). For the exploration-sample group, the areas under the curve for the parameters of MR R2* mapping were 0.55, 0.60, 0.83, 0.64, 0.88 and 0.83 for R2*_base, R2*_1cyc, R2*_2cyc, R2*_{(1cyc-base)/base}, R2*_{(2cyc-base)/base} and R2*_{(2cyc-1cyc)/1cyc.} For the validation-sample, R2*_{(2cyc-base)/base} better predicted progression-free survival (p = 0.03) than RECIST and other R2* mapping parameters with a lower p value. Assessing aATT outcome based on changes in the R2* value between baseline and second treatment is more accurate than assessment at other time-points and assessment based on the RECIST. (orig.)