Course of size and density of metastatic renal cell carcinoma lesions in the early follow-up of molecular targeted therapy.

OBJECTIVE: Imaging-based monitoring of molecular therapies in oncology remains a challenge. Molecular therapies might have more pronounced effects on lesion density than on lesion size. We analyzed changes in lesion diameter and density in patients with metastasized renal cell cancer (mRCC) in the early follow-up of targeted therapy and compared size-based measurements according to Response Evaluation Criteria in Solid Tumors (RECIST) with size- and density-based response evaluations according to the Choi criteria.

PATIENTS AND METHODS: A total of 22 patients treated with sorafenib (800 mg/d) were retrospectively analyzed. Relative changes (in %) in the greatest diameter and density of defined neoplastic "target lesions" were determined 8 weeks and 1 year after start of therapy in relation to a pretherapeutic baseline investigation. Data were analyzed according to RECIST (ver. 1.0), and results were compared with the response assessment based on Choi. Median survival was determined for all subgroups according to Choi or RECIST at the 8-week and 1-year follow-up.

RESULTS: Applying RECIST, 18 patients (82%) demonstrated stable disease (SD) 8 weeks after the start of targeted therapy, 3 patients (14%) partial response (PR), and 1 patient (4%) progressive disease (PD). Partial responders at 8 weeks had a median survival of 48 months. After 1 year, 59% of all patients still showed SD. Applying Choi, 15 patients (68%) showed PR 8 weeks after the start of therapy, 5 patients (23%) SD, and 2 patients (9%) PD. After 1 year, PR was still the predominant response group (64% of the patients). Partial responders after 8 weeks had a median survival of 18 months.

CONCLUSION: Choi defined more patients as partial responders at early stages of therapy than RECIST, but this was not an effective selection for patients with prolonged median survival. Evaluation of a larger patient cohort will further clarify the role of combined size- and density-based follow-up strategies in targeted therapy of mRCC.