Prospective Evaluation of Changes in Tumor Size and Tumor Metabolism in Patients with Advanced Gastric Cancer Undergoing Chemotherapy: Association and Clinical Implication

A change in tumor size is a well-validated and commonly used value for evaluating response to chemotherapy in cancer. Metabolic changes induced by chemotherapy are related to prognosis in several tumor types. However, the clinical implication of metabolic changes in patients with advanced gastric cancer (AGC) undergoing chemotherapy remains unclear. We aimed to evaluate response of tumor size and metabolism in AGC during chemotherapy and to reveal the relationship between them in view of their impact on patient survival. Methods: We prospectively enrolled patients with AGC before the initiation of first-line palliative chemotherapy. Using baseline and follow-up contrast-enhanced CT and F-18-FDG PET, we assessed the tumor diameter, SUVmax, and total lesion glycolysis in each lesion and their changes during chemotherapy at the same time. We included all lesions with the maximal longest diameters over 1 cm on CT, and each lesion was evaluated by matched F-18-FDG PET. We analyzed the association between changes in tumor metabolism and tumor size and performed outcome analysis on overall survival (OS) and progression-free survival (PFS). Results: Seventy-four patients were enrolled, and the number of all lesions included in this study was 620. Compared with adeno-carcinomas, poorly cohesive carcinomas demonstrated lower SUVmax irrespective of tumor size (P < 0.001). Human epidermal growth factor receptor 2 (HER2)-positive tumors showed higher SUVmax than HER2-negative tumors (P = 0.002). The changes in SUVmax due to chemotherapy had a linear correlation with the changes in tumor size of each lesion, and a 30% tumor size reduction was associated with a 50% SUVmax reduction (P < 0.001). Total lesion glycolysis changes also correlated with tumor size changes (P < 0.001). Better OS and PFS were obtained in patients with both tumor size and SUVmax reduction than in patients with either size or SUVmax reduction only (OS, P = 0.003; PFS, P = 0.038). Conclusion: Changes in tumor metabolism induced by chemotherapy correlated with changes in tumor size in AGC. Considering both changes in metabolism and size could help predict a more accurate prognosis for AGC patients undergoing chemotherapy.