Systemic therapies and primary tumour downsizing in renal cell carcinoma: a real-world comparison of anti-angiogenic and immune checkpoint inhibition regimens

Purpose To investigate responses in the primary tumour to different systemic treatment regimens in patients with metastatic renal cell carcinoma (mRCC). Methods A single-centre retrospective analysis of treatment-naive mRCC patients without prior nephrectomy receiving VEGF tyrosine kinase inhibitors (VEGF only), immune checkpoint inhibitors (IO only), or combinations thereof (IO + VEGF). The primary outcome was the rate of partial response in the primary tumour (primary tumour PR, ≥ 30% diameter reduction). Secondary outcomes were time to best primary tumour diameter change, overall survival (OS) and progression-free survival (PFS) by Kaplan–Meier analysis. Predictors of survival outcomes were explored by Cox proportional hazards regression analysis. Results The rate of primary tumour PR was 14% for VEGF only (4/28 patients), 22% for IO only (5/23) and 50% for IO + VEGF (7/14), with median best primary tumour diameter change of − 8.0%, + 5.1%, and − 31.1% respectively, and median time to best primary tumour diameter change of 3.2, 3.0 and 6.9 months respectively. Median OS was significantly greater with IO + VEGF compared to VEGF only (HR 0.45, p = 0.04) and non-significantly greater compared to IO only (HR 0.46, p = 0.06). In multivariable analysis, primary tumour PR was the only response variable significantly associated with both OS (adjusted HR 0.32, p = 0.01) and PFS (adjusted HR 0.29, p