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

Abstract

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. <b>Methods:</b> We prospectively enrolled patients with AGC before the initiation of first-line palliative chemotherapy. Using baseline and follow-up contrast-enhanced CT and ¹⁸F-FDG PET, we assessed the tumor diameter, SUV_max, 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 ¹⁸F-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). <b>Results:</b> Seventy-four patients were enrolled, and the number of all lesions included in this study was 620. Compared with adenocarcinomas, poorly cohesive carcinomas demonstrated lower SUV_max irrespective of tumor size (<i>P</i> < 0.001). Human epidermal growth factor receptor 2 (HER2)-positive tumors showed higher SUV_max than HER2-negative tumors (<i>P</i> = 0.002). The changes in SUV_max 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% SUV_max reduction (<i>P</i> < 0.001). Total lesion glycolysis changes also correlated with tumor size changes (<i>P</i> < 0.001). Better OS and PFS were obtained in patients with both tumor size and SUV_max reduction than in patients with either size or SUV_max reduction only (OS, <i>P</i> = 0.003; PFS, <i>P</i> = 0.038). <b>Conclusion:</b> 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.