BACKGROUND: Lavage cytology is a method to detect cancer cells released within the abdominal cavity. It has been widely utilized, in particular, for gastric cancer. However, its clinical significance has not yet been determined in colorectal cancer. OBJECTIVE: This study aimed to investigate the frequency of lavage cytology positivity and its influence on the prognosis of patients with colorectal cancer. DESIGN: This is a single-institution retrospective observational study. SETTING: This study was conducted at a comprehensive cancer center. PATIENTS: We retrospectively analyzed 3135 colorectal cancer cases from 2007 to 2013 at our institution. Intraoperative peritoneal washing cytology was performed just after the start of the operation. Fluids were centrifuged for 5 minutes at 2500 rotations per minute, cell pellets were smeared on microscope glass slides, and Papanicolaou staining was performed. MAIN OUTCOME MEASURES: The primary outcome was the 5-year overall survival rate. The secondary outcome was the 5-year recurrence rate. RESULTS: Lavage cytology positivity was detected in 19 (2.0%) and 86 (16.9%) cases of stage III and IV colorectal cancer; however, no positive cases were found in stage I and II colorectal cancer. Lavage cytology positivity was an independent prognostic factor in stage III and IV colorectal cancer in the multivariate analysis (5-year mortality HR 3.59 [1.69-7.64] in stage III, 2.23 [1.15-4.31] in stage IV). The prognosis of the 5-year survival rate was significantly worse in the lavage cytology-positive group in stages III and IV. In terms of recurrence, the results of the lavage cytology-positive group in stage III were similar to those of the lavage cytology-positive/negative group in stage IV (73.7%, 70.0%, and 75.0%). LIMITATIONS: This study was limited by its retrospective study design. CONCLUSIONS: Lavage cytology positivity is an independent prognostic and regulatory factor of stage IV colorectal cancer. See Video Abstract at http://links.lww.com/DCR/B770.
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