The current threshold for early tumor shrinkage used to predict outcomes in patients treated for metastatic renal cell carcinoma (mRCC) may not be optimal, according to new findings presented at the American Society of Clinical Oncology annual meeting in Chicago.

In a study of 4,736 mRCC patients, Viktor Gruenwald, MD, and colleagues at the Medical School of Hannover in Hannover, Germany, demonstrated that early tumor shrinkage of 7% or 8% provides the optimal cut-off for predicting progression-free and overall survival, and suggested that the conventional 30% tumor shrinkage threshold is too high.

The researchers used data from Pfizer-sponsored clinical trials with sorafinib, axitinib, sunitinib, interferon-alfa, and temsirolimus. The researchers evaluated early tumor shrinkage at the first post-baseline scan. They classified patients as responders if progression-free and overall survival times (7 and 20 months, respectively) were above the median.

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Of the entire cohort, 67% were treatment naïve and 89% had clear-cell histology.