Conversion therapy for stage IV gastric cancer—the present and future

Gastric cancer (GC) is the sixth most common form of cancer and the fourth most common form of cancer-related death in spite of efforts that have increased the frequency of its early diagnosis and improved intensive treatments (1). The incidence rate of gastric cancer in East Asian countries such as Japan, Korea and China is higher than that in Western countries. Chemotherapy is applied as the first treatment for metastatic and recurrent gastric cancer, even in cases that include a new treatment with a targeted therapy for HER2. The overall survival time remains at 16 months (2-6). In order to further improve the survival of stage IV gastric cancer patients, new therapeutic approaches should be considered (7,8). Conversion therapy for gastric cancer is one of the topics in this issue and successful treatment results have been reported (9-15). Although conversion therapy looks promising, it has not been scientifically proven due to its complicated nature and the fact that the number of candidate patients is too small to carry out a randomized control trial (RCT). Moreover, the following issues remain to be clarified: (I) what is the definition of conversion therapy? (II) What is the indication for the operation (liver, LN, peritoneal, or distant metastasis)? (III) What is the best chemotherapy regimen? (IV) What is the best timing of the operation (when the patient has stable disease or when it is regrowing)? (V) Is postoperative chemotherapy necessary? (VI) Is an R0 operation necessary?