Peritoneal wash cytology plays a pivotal role in the decision for gastric cancer treatment because advanced gastric cancer often turns out incurable with peritoneal metastasis. Molecular detection of minimal cancer cells from peritonea] washings may overcome the sensitivity boundary of conventional cytology and contribute to the prediction of the disease outcome. To select marker candidates out of ten thousands of genes, we performed microarray analyses in 12 gastric cell lines and 8 peritonea] washings of early stage cases. With 40 candidates selected by the above expression profiling, RT-PCR in 16 representative peritoneal wash samples was performed to identify genes specific to cytology positive samples. The finally selected five genes, CK20, FABP1, MUC2, TFF1, and TFF2, were then evaluated for their utility as a marker for minimal residual disease in 99 peritoneal wash samples. Nested RTPCR using the five genes showed positive results highly specific to incurable cases (91-100%). With a high specificity, the combination of these five genes succeeded in identifying 6 out of 20 (30%) additional patients with all types of early recurrence that could not be predicted by the conventional method. The six newly identified recurrences included four non-peritoneal ones, showing that RT-PCR using the five genes without a real-time quantitative PCR technique contributes to the detection of minimal residual disease. (C) 2003 Elsevier Inc. All rights reserved.