Application of the One-step Nucleic Acid Amplification (OSNA) Assay to Detect Free Cancer Cells in the Peritoneal Washing of Gastric and Colon Cancer Patients

The one-step nucleic acid amplification (OSNA) assay is an emergent tool to detect cancer cells in the lymph nodes of several human malignancies including gastrointestinal tumors. The technique identifies and amplifies CK19 mRNA expressed by epithelial cells and has proven easy, rapid, and effective in detecting metastatic cells in lymph nodes. We hypothesized that this methodology could be used to detect free tumor cells in the peritoneal fluid of patients with gastric and colon cancers.

Before the start of the study, five patients suffering of peritoneal carcinomatosis with ascitis (2 from gastric and 3 from colon cancer) served as control. In all five control patients with overt peritoneal metastases, peritoneal washing was positive both cytology and OSNA examination (ranging from 200 to 2,000,000 cCP/µL), showing that OSNA assay is able to identify free cancer cells in a fluid (sensitivity 100%).

A series of 108 consecutive oncological patients (44 gastric and 64 colon cancers) undergoing surgery entered the study. In each patient peritoneal washing was submitted to both traditional cytology and OSNA examination.

The OSNA assay was positive in sixteen patients (14.8%) ranging from 200 to 1,4000,000 cCP/µL. Six gastric cancer patients (13.6%) and ten colon cancer patients (15.6%), with no evidence of peritoneal diffusion, showed free cancer cells in the peritoneal lavage fluid. On the contrary, routine cytologic examination was positive in only four patients (3.7%; two gastric and two colon cancers) who were simultaneously positive at OSNA assay (twelve false negative cases, cytology sensitivity 57.1% assuming OSNA results as true positive cases).

This study suggests that OSNA assay offers a significant advantage over conventional cytology and shoul be widely used to identify gastrointestinal cancer patients at high risk of peritoneal diffusion.