Viktor Grunwald, et al. - Researchers sought to validate the role of early tumor shrinkage (eTS) in first-line treatment among patients with metastatic renal cell carcinoma from the COMPARZ study. Patients treated with sunitinib or pazopanib were analyzed for tumor response according to RECIST 1.0. eTS was defined as tumor shrinkage by ≥ 10%. eTS ≥ 10% had prognostic relevance in mRCC and reflected a putative tool to guide future clinical treatment; in metastatic renal cell carcinoma (mRCC), eTS ≥ 10% had prognostic relevance in mRCC and reflected a putative tool to guide future clinical treatment.