Gastric cancer (GC) remains one of the most common causes of cancer-related mortality worldwide. Surgery has always been considered as the most effective treatment for GC. Peritoneal metastasis is the common pattern of postoperative recurrence, especially patients with T4 stage or serosal invasion. What is worse, patients with peritoneal metastasis have a poor prognosis. However, it is often difficult to diagnose peritoneal metastasis at an early stage. As we know, the implantation of peritoneal free cancer cells exfoliating from serosa-invasive tumors is main reason of peritoneal seeding. Cytological examination of peritoneal lavage fluid is always performed to predict peritoneal micrometastases. However, more than half of patients with negative cytological results develop peritoneal recurrence. Low sensitivity and poor negative predictive value of this method have heralded the development of advanced techniques in detecting peritoneal free cancer cells.