Role of FDG PET/CT in assessing response to targeted therapy in metastatic lung cancers: Morphological versus metabolic criteria.

Introduction: Targeted therapeutic agents are indicated in metastatic lung cancers. These being receptor specific therapies, manifestation of response can be best assessed by estimating the metabolic activity of tumor, rather than the size. This retrospective analysis studied metabolic and morphological response on Positron Emission Tomography (PET) and Computed Tomography (CT), respectively to these agents.
Materials and Methods: Thirty-one patients (23 males, 8 females with an age range of 42-77 years) with Epidermal Growth Factor Receptor (EGFR) positive metastatic lung cancer on Gefitinib, who underwent PET/CT, at baseline and at 4-6 weeks, were assessed by Response Evaluation Criteria In Solid Tumors [RECIST] 1.1 and European Organization for Research and Treatment of Cancer (EORTC) criteria.
Results: Concordance between RECIST 1.1 and EORTC was seen in 26 (83.7%) patients. Discordance was seen in 5 (16.3%) patients. In patients with discordance, the results were confirmed by follow-up imaging. Metabolic EORTC criteria changed the disease status from stable disease to partial response (3 out of 5) and progressive disease (2 out of 5) in these five patients.
Conclusions: Metabolic criteria using PET/CT could accurately predict response as well as disease progression early in the course of targeted therapy, compared to morphologic criteria. In addition, early metabolic response assessment can predict refractoriness of therapy.