Volumetric tumor growth in advanced non-small cell lung cancer patients withEGFRmutations during EGFR-tyrosine kinase inhibitor therapy

BACKGROUND The objective of this study was to define the volumetric tumor growth rate in patients who had advanced nonsmall cell lung cancer (NSCLC) with sensitizing epidermal growth factor receptor (EGFR) mutations and had initially received treatment with EGFR-tyrosine kinase inhibitor (TKI) therapy beyond progression. METHODS The study included 58 patients with advanced NSCLC who had sensitizing EGFR mutations treated with first-line gefitinib or erlotinib, had baseline computed tomography (CT) scans available that revealed a measurable lung lesion, had at least 2 follow-up CT scans during TKI therapy, and had experienced volumetric tumor growth. The tumor volume (in mm3) of the dominant lung lesion was measured on baseline and follow-up CT scans during therapy. In total, 405 volume measurements were analyzed in a linear mixed-effects model, fitting time as a random effect, to define the growth rate of the logarithm of tumor volume (logeV). RESULTS A linear mixed-effects model was fitted to predict the growth of logeV, adjusting for time in months from baseline. LogeV was estimated as a function of time in months among patients whose tumors started growing after the nadir: logeV = 0.12*time + 7.68. In this formula, the regression coefficient for time, 0.12/month, represents the growth rate of logeV (standard error, 0.015/month; P