PET/CT of Lung Cancer

Abstract

Tumors are highly heterogeneous entities, both morphologically and functionally. This heterogeneity applies to the primary tumor and to systemic metastasis. The tumoral molecular profile not only can change and evolve over time across different pathophysiological states but is also capable of dynamically activating its inherent capacity of acquiring resistance to different treatments. Metabolic and molecular imaging techniques such as positron emission tomography (PET) are capable of interrogating in vivo, in one imaging session, several of the above mentioned processes, highlighting some of the heterogeneous signatures of the lung cancer cell phenotype by using specific positron-emitting radiopharmaceuticals. Several of these PET-based molecular probes are available today to noninvasively interrogate glycolytic activity, cellular proliferation, hypoxia, amino acid transport, receptor expression, and apoptosis, among other processes. 18F-Fluorodeoxyglucose (FDG) is a glucose analogue that is widely used clinically to evaluate regional glucose metabolism in several cancer types. FDG-PET yields functional information based on altered tissue metabolism and is useful for both diagnosing and staging cancer. The basis for the use of PET with FDG is the increased glucose consumption by cancer cells compared to normal tissues. In addition, alterations in tissue metabolism that generally precede changes in tumor size are also reflected by this technique. FDG-PET/CT imaging is a superior clinical tool to accurately assess lung cancer's anatomometabolic phenotype. This molecular imaging technique contributes to the diagnosis and initial staging of lung cancer patients by: (a) improving the characterization of the benign or malignant nature of indeterminate solitary pulmonary nodules; (b) complementing conventional imaging techniques to assess primary tumor extent; (c) assessing lymph node status; and (d) detecting systemic disease. FDG-PET/CT also plays an integral role in the subsequent treatment strategy of lung cancer patients. In this context, PET is used to assess the morphologic-metabolic phenotype of tumoral response to cytotoxic and cytostatic cancer therapies, as well as to radiotherapy, and to detect and characterize locorregional and systemic relapse after treatment. PET/CT imaging without a doubt is here to stay as a highly sensitive molecular imaging pearl that provides anatomo-biological and functional insight into the heterogeneous phenotype of lung neoplasia.