Primary tumor response to targeted agents in patients with metastatic renal cell carcinoma.

BACKGROUND: The recent development of multiple targeted agents for metastatic renal cell carcinoma (mRCC) has changed the treatment paradigm; hence the benefit and optimal timing of cytoreductive nephrectomy is being reevaluated.
OBJECTIVE: To determine primary tumor response to treatment with targeted agents in patients with mRCC. DESIGN, SETTING, AND PARTICIPANTS: We reviewed the clinical and radiographic data of all mRCC patients seen at our institution between November 2004 and December 2009 without prior systemic treatment who received targeted therapy with their primary tumor in situ. MEASUREMENTS: Two independent reviewers measured the diameter of primary and metastatic tumors at baseline and subsequent scans, using Response Evaluation Criteria Solid Tumors (RECIST) v.1.1 to assess disease response. RESULTS AND LIMITATIONS: We identified 168 consecutive patients with a median 15 mo of follow-up and a median maximum tumor diameter of 9.6 cm. Median maximum primary tumor response was -7.1% (interquartile range: -14.0 to -0.1). A total of 61 patients had multiple studies available for evaluation. In 43 patients with <10% decrease in primary tumor within in the first 60 d, median maximum response was -7.2% at 154 d versus -24.5% maximum response at 174.5 d for 18 patients with ≥10% decrease in primary tumor during the initial 60 d.
CONCLUSIONS: Decrease in primary tumor diameter >30% while on targeted therapy for mRCC is rare, with most patients demonstrating minimal or no decrease in primary tumor diameter. Early response predicts a better overall primary tumor response.