Imaging Surrogates of Tumor Response to Therapy: Anatomic and Functional Biomarkers*

This article addresses the current status of quantitative imaging as a surrogate biomarker for the assessment of tumor response to therapy with non–small cell lung cancer as an example. In addition, the article discusses the limitations of conventional response criteria in the new era of molecular-targeted agents for cancer treatment; the increasing need for more accurate and early response-assessment methods, particularly for volumetric CT; new tumor-specific radiotracers and molecular imaging technologies; and the future applications of molecular imaging with PET for studying various features of cancer metabolism, endocrine status, hypoxia, and oncofetal and differentiation antigens.