Background
Peritoneal cytology has been used as a part of the cancer staging of gastric cancer patients. The primary aim of this systematic review was to evaluate the value of peritoneal cytology as part of the staging of gastric cancer and survival prediction. The second aim was to establish if positive cytology may be modified by neoadjuvant therapy, to improve prognosis.

Methods
An electronic literature search was performed using Embase, Medline, Web of Science, and Cochrane library databases up to January 2016. The logarithm of the hazard ratio (HR) with 95% confidence intervals (CI) was used as the primary summary statistic. Comparative studies were used, and the outcome measure was survival in three groups: (1) positive versus negative cytology at staging laparoscopy immediately preceding surgery; (2) effect of neoadjuvant therapy on cytology and survival; and (3) positive cytology in the absence of macroscopic peritoneal disease was compared with obvious macroscopic peritoneal disease.

Results
Pooled analysis demonstrated that positive cytology was associated with significantly reduced overall survival (HR, 3.46; 95% CI, 2.77–4.31; P < 0.0001). Interestingly, negative cytology following neoadjuvant chemotherapy was associated with significantly improved overall survival (HR, 0.42; 95% CI, 0.31–0.57; P < 0.0001). The absence of macroscopic peritoneal disease with positive cytology was associated with significantly improved overall survival (HR, 0.64; 95% CI, 0.56–0.73; P < 0.0001).

Conclusion
This study suggests that patients with initial positive cytology may have a good prognosis following neoadjuvant treatment if the cytology results change to negative after treatment.