Impact of tumor size on survival outcome in metastatic renal cell carcinoma patients (mRCC) treated with targeted therapy.

667 Background: Recent research suggested that patients (pts) with small renal masses (4cm or less) were at low risk of disease recurrence after surgery. The impact of tumor size on survival in mRCC patients treated with targeted therapy (TKI) is unclear. Methods: Two cohorts were identified from the International Metastatic Renal Cell Carcinoma Database Consortium (IMDC). Cohort 1 pts had initial nephrectomy for M0 RCC and subsequently developed metastasis during follow-up. Cohort 2 pts presented with de novo metastasis with or without cytoreductive nephrectomy. Cox regression was performed to assess the associations of primary tumor size (≤4 vs > 4cm) and overall survival (OS) on first line TKI, adjusted for histology, sarcomatoid features, tumor stage, number of metastasis, IMDC risk groups and age at TKI initiation. Results: 4089 pts with mRCC treated with first line TKI had primary tumor size data available. Patient characteristics were generally balanced between tumor size groups (≤4 vs > 4cm), except pts with ≤4cm tumors were more likely to have single metastasis (29% vs 18%, p = 0.001) and less likely to have IMDC poor risk (32% vs 39%, p = 0.04) in pts from cohort 2. For pts from cohort 1, tumor size at initial nephrectomy did not impact OS after TKI initiation (p = 0.689). However, in pts presenting with de novo metastasis (cohort 2), small primary tumors were associated with improved OS after TKI initiation, but only in T1-2 tumors (Table). Conclusions: Tumor size impacts survival outcome with targeted therapy in mRCC patients presenting with de novo metastasis and T1-2 disease. This may need to be taken in consideration in clinical trial designs. [Table: see text]