Extraction and analysis of carcinoembryonic antigen in lymph nodes: a new approach to the diagnosis of lymph node metastasis of colorectal cancer.

Abstract

To detect lymph node metastasis of colorectal cancer, we extracted protein from lymph nodes and determined the concentration of carcinoembryonic antigen. In Experiment 1, a total of 237 lymph nodes from 23 colorectal cancer patients were examined histologically after immersion in 200 microl of saline for 2 hours. Concentrations of protein and carcinoembryonic antigen in each saline sample were determined by protein assay and immunoradiometric assay, respectively. Each value of carcinoembryonic antigen in the saline was divided by extracted protein, and the carcinoembryonic antigen levels in lymph nodes were represented as nanograms per milligram of protein. In Experiment 2, 63 lymph nodes from 8 colorectal cancer patients were cut into 2 pieces and immersed in 1 ml of saline for 15 minutes, and they were subjected to reverse transcriptase-polymerase chain reaction for carcinoembryonic antigen and histologic examination, respectively, after measurement of the carcinoembryonic antigen concentration in the extract. From 236 of 237 lymph nodes in Experiment 1, an average of 3,249.4 microg/ml protein was successfully extracted. Histologic examination revealed that 33 of 236 lymph nodes had colorectal cancer metastases, with a significantly higher concentration of carcinoembryonic antigen on average (655.5 ng/mg protein) than in the 203 lymph nodes without metastasis (18.2 ng/mg protein; P < 0.0001). In Experiment 2, 19 of 63 lymph nodes examined were positive for metastasis in both reverse transcriptase-polymerase chain reaction and histology and showed a significantly higher carcinoembryonic antigen concentration on average (1,003.9 ng/mg protein) than the 42 lymph nodes that demonstrated no metastasis by either method (18.0 ng/mg protein; P < 0.0001). The remaining two lymph nodes, which were positive by reverse transcriptase-polymerase chain reaction but negative by histology, showed high carcinoembryonic antigen concentrations of 514.7 and 61,970.5 ng/mg protein, respectively. This simple method of protein extraction and determination of carcinoembryonic antigen concentration in lymph nodes may provide an alternative tool for the diagnosis of colorectal cancer metastasis.