Background. The development of a sensitive method for the detection of breast carcinoma micrometastases in axillary lymph nodes is reported.
Methods. The method was based on amplification of MUCl mRNA, which encodes a core protein of polymorphic epithelial mucin, by a reverse transcriptase‐polymerase chain reaction (RT‐PCR). Total RNA, which was extracted from a breast carcinoma cell line (MCF‐7), primary breast carcinomas, and axillary lymph nodes, was subjected to analysis of MUCl mRNA expression by the RT‐PCR method.
Results. MUCl mRNA expression was detected by RT‐PCR in MCF‐7 cells and in all 15 primary breast carcinomas but not in control lymph nodes taken from patients with benign diseases. A serial dilution study revealed that MUCl RT‐PCR was a very sensitive method, detecting one MCF‐7 cell per 1,000,000 lymph node cells.
The detection sensitivity of MUCl RT‐PCR method was compared with that of immunohistochemical staining of an epithelial marker (polymorphic epithelial mucin). Fifty axillary lymph nodes were obtained from 15 patients with primary breast carcinomas, and metastasis in each lymph node was investigated by both methods. The immunohistochemical method demonstrated metastasis in nine lymph nodes, and MUCl mRNA was detected in all of them. Of the 41 lymph nodes that were diagnosed to be devoid of metastasis by immunohistochemistry, MUCl mRNA was expressed by 6 but not by the other 35, indicating the presence of micrometastases in these 6 lymph nodes that could be detected only by the MUCl RT‐PCR method.
Conclusions. The MUCl RT‐PCR method is more sensitive than immunohistochemistry for the detection of micrometastases in axillary lymph nodes. This new method would be of practical value in selecting the patients at high risk for relapse from those who are histologically lymph node negative.
A sensitive method for the detection of gastric cancer micrometastases in lymph nodes was developed. The method was based on amplification of keratin 19 mRNA by reverse transcriptase‐polymerase chain reaction (RT‐PCR). Keratin 19 RT‐PCR showed that keratin 19 mRNA was expressed in all 12 gastric cancers, but not in any of 20 normal control lymph nodes, indicating that keratin 19 mRNA is a good target of RT‐PCR for the detection of gastric cancer micrometastases in lymph nodes. Serial dilution studies of RNA extracted from gastric cancers against RNA extracted from control lymph nodes demonstrated that the detection sensitivity of the keratin 19 RT‐PCR method was one cancer cell in 103‐105 lymph node cells. Detectability of lymph node metastases was compared between keratin 19 RT‐PCR and conventional histological examination, using 100 lymph nodes obtained from 12 gastric cancer patients. Keratin 19 mRNA was detected in all of the seven lymph nodes which were historically metastasis‐positive. Of the 93 lymph nodes which were histologically metastasisnegative, 79 were found not to express keratin 19 mRNA but 14 were found to express keratin 19 mRNA, indicating that these lymph nodes contained micrometastases which could not be detected by histological examination. These results demonstrate that keratin 19 RT‐PCR is a more sensitive method than histological examination for the detection of gastric micrometastases in lymph nodes.
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