S-1 and the treatment of gastric cancer with peritoneal dissemination

Peritoneal dissemination is the most common metastatic pattern of gastric cancer. We frequently face the necessity for gastrectomy in the event of gastric stenosis or gastric bleeding. However, the indication for palliative gastrectomy and the effectiveness of palliative chemotherapy are not clear. We retrospectively evaluated the prognostic factors after palliative gastrectomy in 121 gastric cancer patients with peritoneal dissemination. The expression of orotate phosphoribosyl transferase (OPRT) was examined immunohistochemically. The median survival time of all patients after palliative gastrectomy was 8.8 months. In the multivariate analyses, we adjusted the data of 82 patients without liver metastases for the background of 5-fluouracil (5-FU)-based chemotherapy regimen. The analysis revealed that the degree of peritoneal dissemination (multiple vs. a few metastases or cytology-positive; P= 0.01) and chemotherapy (S-1 vs. other 5-FU; P=0.01) were independent predictors of survival. Particularly, S-1 treatment was associated with a more favorable prognosis of the patients with high levels of OPRT expression compared to that of the patients with low expression. Patients with peritoneal dissemination are considered as terminal and inoperable. However, S-1 treatment may improve the survival after palliative gastrectomy in patients selected according to the degree of peritoneal dissemination and high OPRT expression.