Detection of cancer micrometastases in lymph nodes by reverse transcriptase-polymerase chain reaction

There are few DNA-based studies that detect cancer micrometastases in lymph nodes. We have assayed for the specific detection of carcinoembryonic antigen (CEA)-expressing carcinoma cells in the lymph nodes of patients with gastrointestinal or breast carcinomas. A CEA-specific nested reverse transcriptase (RT)-PCR assay was optimized using limiting dilutions of a CEA-positive cancer cell line mixed with normal lymphocytes. The expression of CEA mRNA was studied in 100 carcinoma tissues, 75 normal mucosal tissues, and 15 lymph nodes from patients with cholelithiasis. Each of 117 lymph nodes from 13 patients with carcinoma was divided into two pieces: one was used for histological examination and the other for RT-PCR, and the results were compared. The sensitivity ratio was one CEA-expressing cancer cell detected in 1 x 10(5) normal lymphocytes. All carcinoma tissues and normal mucosal tissues expressed CEA mRNA, while no amplification was detected in any control lymph nodes. Thirty of 117 lymph nodes were histologically involved by carcinoma cells, and all of these yielded the expected product by RT-PCR. Of the remaining 87 histologically negative nodes, CEA mRNA was detected in 47 lymph nodes by RT-PCR. The positive rate increased from 26% by histological examination to 66% by RT-PCR. The assay by CEA-specific nested RT-PCR is not only sensitive but widely applicable for the detection of cancer micrometastases in lymph nodes. This method may lead to an earlier diagnosis and treatment of patients with subclinical lymph node metastasis.