We previously performed a global analysis of the gene expression of
gastric cancer cell lines established from
metastases to the peritoneal cavity with the
cDNA microarray method, which made it possible to analyse the expression of approximately 21168 genes for the identification of novel markers for the detection of
micrometastases in the peritoneal cavity. One of the upregulated genes is
dopa decarboxylase (DDC), which is responsible for the synthesis of the key
neurotransmitters dopamine and serotonine. We have examined its potential as a novel marker for the detection of peritoneal
micrometastases of
gastric cancer.DDC
mRNA in the peritoneal wash from 112
gastric cancer patients was quantified for comparison of
carcinoembryonic antigen (CEA)
mRNA by means of real-time
reverse transcriptase-polymerase chain reaction (RT-PCR) with a fluorescently labelled probe to predict peritoneal recurrence. The quantity of DDC and CEA correlated with wall penetration. Real-time RT-PCR could quantitate 10-10(6) DDC-expressing
gastric cancer cells per 10(7) mesothelial cells. The cutoff value was set at the upper limit of the quantitative value for noncancer patients, and those above this cutoff value constituted the
micrometastasis (MM+) group. Of 15 cases with peritoneal dissemination, 13 were MM+DDC (87% sensitivity), and one of 48 t1 cases was MM+ (98% specificity). DDC levels in peritoneal washes from patients with synchronous peritoneal
metastases were more than 50 times higher than in those from patients without
metastasis (P<0.01). For 15 cases of peritoneal dissemination (seven cases were cytologically positive), DDC was positive in 13 cases (87% sensitivity), but CEA failed to detect
micrometastases in four cases (73% sensitivity), indicating that DDC is in some cases superior to CEA for the detection of peritoneal
micrometastases of
gastric cancer in terms of sensitivity as well as specificity, especially for poorly differentiated
adenocarcinomas. A combination of CEA and DDC improved the accuracy of diagnosis up to 94%. These results suggest that DDC is potentially a novel marker for peritoneal dissemination of
gastric cancer and that quantitative RT-PCR of DDC is reliable and efficient for the selection of patients for adjuvant intraperitoneal
chemotherapy to prevent peritoneal recurrence.