Background: Positive peritoneal cytology confers the same prognosis as clinical stage IV disease in gastric cancer. Conventional cytology examination, however, has low sensitivity. We hypothesize that real-time polymerase chain reaction (RT-PCR) may have increased sensitivity and provide more accurate staging information.
Methods: From February 2007 to April 2009, peritoneal lavage samples were collected prospectively from 156 patients with biopsy-proven gastric cancer undergoing staging laparoscopy. These washings were analyzed by both Papanicolaou staining and RT-PCR for the tumor marker carcinoembryonic antigen (CEA).
Results: Visible peritoneal disease was seen at laparoscopy in 38 patients (LAP+, 24%). Cytology was positive (CYT+) in 23 patients, while RT-PCR was positive (PCR+) in 30. The sensitivity of CYT for the detection of visible disease was 61% compared to 79% for PCR (P = 0.02). No visible peritoneal disease was seen at laparoscopy (LAP-) in 118 (76%) patients. Eight (7%) were CYT+, while 28 (24%) were PCR+. Predictors of PCR positivity included advanced-stage disease (T3-4 vs. T1-2 tumors) and poor pathologic features such as vascular or perineural invasion. Long-term follow-up demonstrated a worse survival of LAP-CYT-PCR+ (P = 0.0003) and LAP-CYT+PCR+ (P = 0.0004) compared to LAP-CYT-PCR- patients. There was no significant difference in survival between CYT-PCR+ and CYT+PCR+ patients. PCR positivity also predicted a higher likelihood of disease recurrence after resection. An R0 resection was performed in 85 LAP- patients (54%): only 1 (1%) was CYT+, while 13 (15%) were PCR+. Of this group, PCR+ demonstrated a worse survival than PCR- patients (P = 0.02). Further analysis showed that, in R0 resection, stage III/IV, CYT- subgroup, PCR+ was associated with a trend towards worse survival (P = 0.09) compared to PCR- patients.
Conclusion: RT-PCR for CEA increases the detection of subclinical peritoneal disease and is more sensitive than cytology. Predictors of positive PCR included advanced-stage disease, vascular invasion, and perineural invasion. PCR positivity was associated with increased disease recurrence and decreased survival. Further follow-up is required to determine if PCR positivity alone is an independent predictor of poor survival in gastric cancer.